Purple Potato Gnocchi with Seared Scallops, Shellfish Bisque and Tarragon | Gnocchi di Patate Viola con Capesante Scottate, Bisque di Crostacei e Dragoncello

Sep 22

11 min read

Purple Potato Gnocchi with Seared Scallops, Shellfish Bisque and Tarragon (Gnocchi di Patate Viola con Capesante Scottate, Bisque di Crostacei e Dragoncello)

This is a plate built on three disciplines that rarely share a pan. The gnocchi are an exercise in restraint, the least flour a potato will tolerate. The bisque is an exercise in extraction, every gram of flavour pulled from shells most kitchens throw away. The scallops are an exercise in timing, ninety seconds of decisive heat. Tarragon ties them together with an anise note unusual in Italian cooking and completely at home here.

The purple potato is not decoration. Violet fleshed varieties are drier and denser than a yellow potato of the same size, so they take less flour to bind, and less flour is the whole argument of good gnocchi. The colour is a bonus: against an orange bisque and the ivory of a seared scallop it reads from across a room. Cooked correctly the gnocchi stay deep violet, while carelessly boiled in unsalted water they leach into a dull grey.

Nothing here is difficult in isolation. What makes it restaurant work is that the bisque must be warm, the gnocchi shaped and the scallops dry before anything goes near the fire, because the final assembly takes under four minutes.

Yield: 4 servings. Prep: 1 hour. Cook: 1 hour 15 minutes. Total: about 2 hours 15 minutes. Difficulty: advanced. Course: primo piatto. Region: modern Italian, with roots in Veneto, Piedmont and Tuscany.

The Story

Potato gnocchi are younger than most people assume. The potato reached Italy in the second half of the sixteenth century and was treated as animal feed or famine insurance for two hundred years afterwards. Only in the nineteenth century, once the tuber had earned a place in the northern kitchen garden, did gnocchi di patate settle into the form we recognise, above all in Veneto, Friuli and Piedmont, where the older gnocchi made with breadcrumbs or semolina slowly gave ground.

Violet fleshed potatoes are an old crop, though not an Italian one. They came from the Andes with every other potato and survived where growers valued flavour over yield. Italy still has its own: the turchesa of the highlands around the Gran Sasso in Abruzzo is a violet skinned, violet fleshed landrace local producers have fought to keep in cultivation. They are floury, low in moisture and slightly sweeter than a common yellow potato, exactly the profile a gnocco wants.

The scallop is Venetian territory. Capesante have been landed in the northern Adriatic for centuries and the name is a pilgrim's souvenir: the fluted shell was the badge carried home from Santiago de Compostela. Tarragon belongs to Siena, one of the few places in Italy where the herb is genuinely traditional rather than borrowed from France. Putting it with shellfish is a modern move, but a defensible one.

Ingredients

For the purple potato gnocchi

Purple potatoes, floury variety, 1 3/4 lb (800 g), similar size
All purpose flour, 1 1/2 cups (190 g), plus more for the bench
Egg yolk, large, 1
Fine sea salt, 1 tsp (6 g)
Freshly grated nutmeg, 1 small pinch

For the shellfish bisque

Shrimp, prawn or langoustine shells and heads, 1 lb (450 g)
Extra virgin olive oil, 2 tbsp (30 ml)
Yellow onion, small, 1
Carrot, small, 1
Celery stalk, 1
Tomato paste, 1 tbsp (16 g)
Brandy, 2 tbsp (30 ml)
Dry white wine, 1/2 cup (120 ml)
Water or light fish stock, 4 cups (950 ml)
Bay leaf, 1
Black peppercorns, 6
Heavy cream, 2 tbsp (30 ml)
Unsalted butter, cold and diced, 2 tbsp (28 g)
Fine sea salt, to taste

For the scallops

Large dry packed sea scallops, 12, about 12 oz (340 g)
Extra virgin olive oil, 1 tbsp (15 ml)
Unsalted butter, 1 tbsp (14 g)
Fine sea salt, to taste
Freshly ground white pepper, to taste

For finishing

Fresh tarragon leaves, 2 tbsp, loosely packed
Unsalted butter, cold, 1 tbsp (14 g)
Finely grated lemon zest, from 1/2 lemon
Coarse salt for the gnocchi water, 2 tbsp (30 g) per 4 quarts (3.8 l)
Extra virgin olive oil, a few drops per plate

Preparation

Step 1

Bake the potatoes, never boil them. Heat the oven to 400°F (200°C). Prick the potatoes once each and bake them on the rack, unwrapped and unsalted, for 50 to 60 minutes until a skewer slides through without resistance. Boiling drives water into the flesh and every extra gram must later be absorbed by extra flour, the commonest reason gnocchi turn heavy. Baking drives water out instead.

Step 2

Rice the flesh hot and let it steam dry. Split each potato and scoop the flesh straight into a ricer or food mill fitted with the fine disc, working fast enough that you handle hot potato rather than warm. Spread it loosely over a tray and leave it three or four minutes untouched, until steam stops rising. Do not mash or blend: a blade ruptures the starch granules and turns the dough gluey.

Step 3

Make the dough with the least flour it will take. Gather the cooled potato into a loose mound, scatter over salt and nutmeg, add the egg yolk and two thirds of the flour. Fold and press with the flat of your hand for under a minute, adding flour only where the dough sticks to the bench. Stop while it is slightly tacky and just coherent.

Step 4

Shape and rest the gnocchi. Cut the dough into four, roll each piece into a rope about 3/4 inch (2 cm) thick on a floured bench and cut into equal lengths. Roll them down the back of a fork or a gnocchi board with a light thumb, so each carries ridges on one side and a hollow on the other, then set them well spaced on a floured tray. Those ridges are what holds a thin bisque against the gnocco. Rest uncovered 20 minutes.

Step 5

Extract the bisque. Heat the olive oil in a wide heavy pot over high heat and add the shells and heads. Press them hard with a wooden spoon and let them colour deeply, 6 to 8 minutes, until the pot smells roasted rather than raw. Add the diced onion, carrot and celery, drop to medium and sweat 6 minutes, then stir in the tomato paste and cook it out. Add the brandy, let it burn off, add the wine and reduce by half. Pour in the water with bay and peppercorns and simmer gently 40 minutes, never boiling hard.

Step 6

Blend, strain and reduce. Blitz the pot briefly with a stick blender to break the shells further, then pass everything through a colander, pressing hard. Pass the liquid again through a fine mesh sieve lined with muslin. Reduce in a clean pan to about 1 1/4 cups (300 ml), until it coats a spoon lightly. Season only now: a bisque salted early becomes inedible once it has lost two thirds of its volume.

Step 7

Finish the bisque and sear the scallops. Off direct heat, whisk the cream into the reduced bisque, then the cold butter a cube at a time so it emulsifies into a glossy sauce rather than an oil slick. Hold it warm, never simmering. Pat the scallops bone dry, season and sear in a very hot pan with the olive oil for 60 to 75 seconds, until a hard amber crust forms, then turn, add the butter and baste for 30 seconds.

Step 8

Boil the gnocchi and finish them in the pan. Bring 4 quarts (3.8 l) of water to a rolling boil and add 2 tablespoons (30 g) of coarse salt. Purple potatoes taste flat and lose colour in underseasoned water, so do not economise. Drop the gnocchi in and lift each out with a spider about 20 seconds after it rises, set through but still tender. Slide them into a wide pan with four tablespoons of the gnocchi water and the cold butter, swirl over low heat for 30 seconds until the liquid turns silky and clings, then add the tarragon and lemon zest off the heat.

Plating

Warm the plates properly, to around 140°F (60°C). Gnocchi hold very little heat and the bisque is an emulsion that tightens as it cools, so a cold plate costs you both within a minute. Use a wide shallow bowl with a flat base, so the sauce pools rather than drowns.

Pour about three tablespoons of warm bisque into each bowl and tilt once to spread. Spoon the dressed gnocchi into the centre in a loose mound, seven or eight per person, sitting partly in the sauce rather than swimming. Arrange three scallops around them, seared side up and never sauced over, because the crust goes soft the instant it is covered.

Finish with a few whole tarragon leaves and a thread of good olive oil around the edge. No cheese: grated pecorino or parmesan on a shellfish sauce flattens the sweetness of the scallop. Serve immediately.

Professional Technique

The governing technique is the double extraction of the shells. Most home bisques stop at a simmer, which pulls out water soluble flavour and leaves everything bound up in the fat and the shell. Roasting the shells hard first produces the Maillard compounds that give a bisque its depth, and the carotenoid pigments that give it colour are fat soluble, which is why the oil turns orange in the pot and must stay in the sauce. Blending the shells after the simmer, then straining twice, recovers flavour a gentle strain leaves in the bin.

The second technique is the butter emulsion. Cold butter whisked into a reduced liquid below a simmer suspends the fat as microscopic droplets held by proteins already in the stock, giving body and shine with no flour and almost no cream. It is fragile: let it boil and it breaks into a greasy pool in seconds. Hold it between 150°F and 160°F (65°C and 70°C), off the burner. The scallop demands the opposite kind of attention, a protein with a very narrow window: roughly three quarters water, its fibres contract above 130°F (55°C) and force that water out, so only a genuinely hot dry pan and a genuinely dry scallop will build a crust before the interior is ruined.

Texture and Moisture Control

Every failure in this dish is a moisture failure. Water in the potato forces flour into the dough and flour builds gluten, so baking rather than boiling, ricing hot, steam drying and then adding minimum flour is one continuous strategy to keep water out. A correctly made gnocco is barely coherent on the bench. If your dough feels like pasta dough, it is already too far gone.

In the sauce the variable is concentration. Reduce too little and the bisque runs off the gnocchi into a watery ring at the edge of the bowl, reduce too far and the salt concentrates, the emulsion refuses to hold and the sauce turns to paste. Aim for a liquid that coats the back of a spoon and closes slowly when you draw a finger through it. Keep gnocchi water beside the pan: salted, starchy and warm, it is the right tool for loosening a sauce gone too far.

On the plate three temperatures diverge fast. Gnocchi leave the water near 200°F (95°C) with almost no thermal mass and shed heat in a minute, the bisque must stay above 140°F (60°C) to keep its shine, and the scallops keep cooking for thirty seconds after they land, so pull them a shade under.

Professional Mise en Place

The bisque and the gnocchi are both done in advance and the last four minutes contain everything else.

Equipment and tools

Potato ricer or food mill with a fine disc, never a blender or a masher
Wide heavy pot for the shells, plus a stick blender
Colander and a fine mesh sieve with muslin for the double strain
Heavy skillet, carbon steel or stainless, for the scallops
Spider skimmer, wide sauté pan for finishing, instant read thermometer

Prepared ahead

Bisque reduced and strained, up to 3 days refrigerated, finished only at service
Gnocchi shaped and frozen solid on a tray, then bagged, up to 1 month
Scallops trimmed of the side muscle, uncovered on a rack in the refrigerator for 1 hour
Tarragon picked and kept between damp paper, lemon zested at the last moment
Gnocchi water at a rolling boil and correctly salted before anything is seared

Service setup

Bisque warm off direct heat, whisked briefly before it goes into the bowls
Bowls warming at 140°F (60°C)
Scallop pan fully preheated, scallops on a dry tray beside it
Finishing butter cold and cubed, gnocchi water within reach
Everything plated in one pass: bisque, gnocchi, scallops, tarragon, oil

Chef Tips

Buy your potatoes in one size. A tray holding one large and one small gives you one perfectly baked tuber and one still dense in the middle, and the underdone one holds water that ruins the batch of dough.

Freeze the gnocchi rather than refrigerating them. Shaped gnocchi held in the refrigerator weep, stick to the tray and go grey at the edges within hours. Frozen solid and then bagged, they keep a month.

Never throw away a shell. Every time you buy shrimp or prawns, peel them, bag the heads and shells and freeze them. Two or three such bags make this bisque at no cost beyond the aromatics.

Taste the bisque before you reduce it and again after. The flavour does not simply intensify, it changes shape: sweetness comes forward, the roasted note deepens and any bitterness from scorched shells becomes obvious. Catching that halfway leaves you time to dilute and rebalance.

Common Mistakes

Boiling the potatoes. Water goes into the flesh, flour comes into the dough to compensate, and the gnocchi come out as dense pellets. Bake them dry on the oven rack instead, and the whole dish improves before you have touched anything else.

Working the dough like bread. Kneading develops gluten and gluten makes gnocchi chewy. Fold and press for under a minute, stop while the dough is still slightly tacky, and accept that it will feel too soft.

Salting the bisque early. A liquid reduced from 4 cups to 1 1/4 cups concentrates its salt more than threefold. Season only after the reduction is finished, or there is nothing to be done with the result.

Using wet packed scallops. Treated scallops carry added water, exude it into the pan and steam instead of searing, however hot the pan is. Buy dry packed, and dry them further on a rack in the refrigerator.

Overcooking the gnocchi. They are ready about 20 seconds after they float, not when a timer says so. Left longer they absorb water, swell and collapse when you move them into the sauce.

Wine Pairing

Vermentino di Gallura DOCG: Grown on decomposed granite in northern Sardinia, this is the most instinctive match here. Its saline edge meets the shellfish directly and its citrus acidity cuts the butter in the bisque without stripping sweetness from the scallop. The bitter almond finish gives the tarragon something to lean against.

Greco di Tufo DOCG: A far more structured white than its colour suggests, with real weight, a stony smoky character from the volcanic soils of Irpinia and enough grip for a reduced crustacean sauce. Where a lighter wine vanishes under the bisque, this one holds its shape and answers back.

Verdicchio dei Castelli di Jesi Classico Riserva DOCG: The Riserva bottlings carry extra time on the lees, giving a creamy texture that mirrors the emulsified butter, while the high acidity typical of the grape keeps everything fresh. Its signature bitter almond finish sits beautifully alongside anise.

Franciacorta DOCG: Where richness is the risk, a traditional method sparkler is the reliable answer. Bubbles and low dosage scrub the palate between mouthfuls of buttery bisque, and the bready autolytic character picks up the toasted crust on the scallops.

Etna Bianco DOC: Carricante grown on the volcano gives a taut, high acid wine with a flinty core and a citrus peel bitterness that suits shellfish better than fruit driven whites do. Its slightly severe character is the one austere element on an otherwise generous plate.

Storage & Reheating

The bisque is the one component that genuinely stores. Reduced and strained but not yet finished with cream and butter, it keeps in an airtight container in the refrigerator for 3 days and freezes for 3 months, ideally in an ice cube tray. Rewarm gently and only then whisk in the cream and cold butter, since a bisque already emulsified and chilled will not come back cleanly.

Raw shaped gnocchi freeze better than they refrigerate. Spread them apart on a floured tray, freeze until hard, then bag them for a month. Cook from frozen in heavily salted boiling water, adding 30 seconds. Cooked gnocchi do not store: refrigerated overnight they turn dense and waterlogged, and no reheating recovers them.

Seared scallops should be eaten within minutes and never reheated, since a second exposure to heat forces out the remaining moisture and leaves them tough. With leftovers, refrigerate for a day, slice thinly and serve cold over salad. To rescue a plated portion, cover it in a pan with a splash of water over the lowest heat for two minutes.

Nutrition

Per serving, based on 4 portions:

Calories: 610 kcal
Total Fat: 24 g
Saturated Fat: 12 g
Trans Fat: 0 g
Unsaturated Fat: 10 g
Cholesterol: 135 mg
Sodium: 780 mg
Total Carbohydrates: 65 g
Fiber: 5 g
Total Sugars: 4 g
Added Sugars: 0 g
Protein: 31 g
Lactose: 0.9 g
Principal micronutrients: vitamin B12, selenium, zinc, phosphorus, potassium, anthocyanins from the purple potato