For the Gribiche

1. Make the gribiche a day in advance if you can, to let the flavours really fuse together.
2. Hard-boil the egg for 10 minutes, then chill in iced water.
3. Peel and finely dice the shallot along with the cornichons. Finely chop the herbs.
4. Peel and chop the egg, then add to a bowl with the diced shallot and cornichons, the lemon zest and juice, chopped herbs, capers and mayonnaise. Combine gently, then taste to make sure you’re happy with the seasoning before chilling in the fridge.

For the Simple Mayonnaise

1. Use a large whisk to mix the egg yolks, vinegar and mustard together in a round-bottomed bowl, then gradually start whisking in the vegetable oil. If you find that the mayonnaise is thickening too quickly and there’s still plenty of oil left to add, then a spoonful of water will help regulate the consistency.
2. Continue whisking and adding oil until it is all used up and emulsified, then season to taste with salt.
3. Store in an airtight container in the fridge for up to 3 days.

For the Turbot and Leeks

1. Trim the very green tops away from the leeks and give them a good wash. Put the leeks on a hot barbecue grill or in a dry pan over a medium-high heat and cook for 8 minutes or so, turning every few minutes, until the leeks are heavily blackened all over. Leave to rest for 5 minutes. Prick with a knife – they should be soft with a little resistance. If they feel undercooked, bake in a hot oven (220°C) for 4–5 minutes. Once you’re happy that they’re cooked through, leave the leeks to cool completely while you cook the fish.
2. Heat the vegetable oil in a large non-stick frying pan over a medium-high heat and preheat the oven to 80°C, or its lowest possible setting. Season the fish with salt and place in the pan, dark-skin-side first. Give them a minute or two then turn over to the white side of the fish. Keep a close eye on the temperature of the pan – if it starts to smoke, turn it down; if it seems to be cooking a little slowly, turn it up. You want a consistent sizzle.
3. At this stage, add the butter, thyme and garlic. Start basting the turbot with the butter until it starts to froth and caramelise. Squeeze in the lemon juice and leave the lemon half in the pan. Transfer the fish to a small roasting tray and leave to rest for 4–5 minutes. Use a probe to test the turbot – it should be around 30°C. Resting the fish halfway through cooking like this gives both you and the protein time to rest and check on the other elements of your dish. To finish the cooking, pop it in the low oven for 10 minutes or so, or until you reach an internal temperature of 45°C.
4. To build the dish, remove the burnt layers of leek, then split the leek open and season with olive oil, Maldon salt and some of the fish cooking butter. Add the fish and finish with a large spoonful of gribiche on the side.