Stuffed Halibut with Mussel Veil

1. BRINE THE HALIBUT
Combine the water, salt and optional sugar in a non-reactive container and stir until dissolved. Submerge the halibut portions and refrigerate for 15 minutes (no longer — over-brining will turn the texture spongy). Drain, rinse briefly under cold water, and pat completely dry. The brief brine seasons the flesh and tightens the protein.

2. MAKE THE SHRIMP FARCE
Pat the cold shrimp very dry. In a chilled food processor, blitz the shrimp with the salt, white pepper and lemon zest until smooth. Add the egg white and pulse to combine. With the motor running, slowly stream in the cold cream and stop the moment it is just incorporated — over-processing will cause the cream to break. Pass the farce through a fine sieve into a bowl, cover, and chill for at least 30 minutes. Quick test: poach a teaspoon in simmering water for 90 seconds, taste, and adjust seasoning if needed.

3. ROLL THE HALIBUT
Lay each halibut portion between two sheets of cling film and gently pound to an even 4-5 mm thickness, keeping a roughly rectangular shape. Lay each piece on a fresh sheet of cling film. Pipe or spread about a tablespoon of farce in a line along one short edge, then use the cling film to roll the halibut up tightly into a log. Twist the ends of the cling film hard to compact the roll, then knot. Repeat with the remaining portions and chill the rolls for 20 minutes to set the shape.

4. MAKE THE SQUASH-NORI VEIL BASE
Combine the squash, water, thyme, lemon peel and salt in a saucepan. Cover and simmer over medium heat for 15-18 minutes, until the squash is completely tender. Discard the thyme stems and lemon peel. Tip the contents of the pan (squash and all the liquid) into a high-powered blender, add the torn nori, and blend on high until completely smooth. Pass through a fine sieve, pressing firmly. You should have about 330g of strained purée — thin with a little water if necessary.

5. SET THE VEIL
Weigh the strained purée and calculate 1.5% kappa carrageenan by weight (so 5g for 330g of purée). Pour the purée back into a clean saucepan, sprinkle the carrageenan over the surface, and immediately whisk hard for a few seconds to disperse. Bring to a gentle simmer over medium heat, whisking constantly — it should thicken noticeably as it heats. Remove from the heat. Working quickly (kappa sets fast), pour the hot mixture onto a flat, lightly oiled sheet pan or marble slab and spread with an offset spatula into an even layer about 2 mm thick. The veil will set within a couple of minutes at room temperature; chill in the fridge to firm fully.

6. SWEAT THE LEEKS
Melt the butter in a wide sauté pan over low heat. Add the sliced leeks and a pinch of salt, cover, and cook very gently for 15-20 minutes, stirring occasionally, until completely soft and sweet but with no colour. The melted leek base should taste of nothing but concentrated sweet allium and butter.

7. STEAM THE MUSSELS AND RESERVE THE LIQUOR
In a separate pan with a tight-fitting lid, sweat the diced shallot in a knob of butter for one minute. Add the wine, bring to a brisk boil, then add the mussels, cover, and steam for 3-4 minutes, shaking the pan, until all the shells have opened. Tip into a colander set over a bowl to catch the liquor. Discard any unopened mussels, pick the meat from the rest, and keep warm. Strain the liquor through a fine sieve lined with muslin or kitchen paper — you can use this in place of the bottled clam juice in the sauce if you prefer.

8. TOAST THE HAZELNUTS
Toast the blanched hazelnuts in a dry pan or in a 350°F (180°C) oven for 6-8 minutes until golden and fragrant. Cool, then crush roughly with the side of a knife or in a mortar — you want texture, not powder.

9. COOK THE HALIBUT
Sous vide method (recommended): set a water bath to 130°F (54°C). Vacuum-seal the cling-wrapped halibut rolls in a single layer (the rolls are already wrapped, so a single sealed bag is fine) and cook for 22 minutes.
Stovetop method: bring a deep pan of water to 145-150°F (63-65°C), monitored with a probe thermometer. Slip the cling-wrapped rolls in and hold at temperature, adjusting the heat as needed, for 12-14 minutes. The fish should be just opaque all the way through but still glistening.

10. MAKE THE BROWN BUTTER SAUCE
While the fish cooks, melt 100g of the butter in a heavy-bottomed saucepan over medium heat. Continue cooking, swirling the pan, until the milk solids turn deep golden-brown and the butter smells of toasted hazelnuts — about 4-6 minutes. Immediately pour in the clam juice (it will splutter dramatically; stand back). Reduce by about a third over medium heat, then remove from the heat and whisk in the remaining 40g of cold butter, cube by cube, to mount the sauce to a glossy emulsion. Finish with the lemon juice and salt to taste. Keep warm but do not let it boil again.

11. CUT THE VEIL
Lift the set veil onto a board with the offset spatula. Cut into six panels, each large enough to drape completely over a plated portion (roughly 12 x 8 cm / 5 x 3 inches). Keep at cool room temperature — kappa veils stay supple at room temperature but become brittle if over-chilled.

12. PLATE
Spoon a generous tablespoon of melted leeks into a line across the centre of each plate. Scatter mussels and hazelnuts over the leeks. Unwrap the halibut rolls and slice off the twisted ends; place each roll on top of its garnish bed. Drape a panel of veil gently over the entire arrangement — the veil should completely cover the fish and most of the garnish, leaving just enough exposed at the edges to suggest what's underneath. Spoon the warm clam-brown butter sauce around (not over) the veil. Finish with a scatter of chives if using and serve immediately.

CHEF'S NOTES
The brine is non-negotiable: halibut tastes noticeably better after a brief 15-minute soak in 4% brine. Skip it and the dish loses depth. Kappa carrageenan is the gelling agent here — it produces a brittle, glass-clear sheet quite different from the soft wobble of gelatin. If you cannot source it, a softer veil can be made with sheet gelatin: bloom 4 sheets (8g) in cold water, drain, then dissolve into the warm strained purée off the heat. Pour onto an oiled tray to a 2-3 mm depth and chill for at least 2 hours until set; the gelatin veil must stay refrigerated until just before service. Don't grind the hazelnuts too fine — the textural surprise is the whole point. The halibut roll is forgiving in shape and size: any firm, mild white fish (turbot, monkfish loin, or wild striped bass) works in place of halibut, but avoid thin or flaky fish.