Make a vinaigrette of the olive oil, tarragon vinegar, water and a pinch of salt. Sprinkle the turbot on both sides with the vinaigrette and then grill it on The Bastard in a fish clip. Keep turning it and then brush the fish with the vinaigrette. Make sure the skin of the belly (the white side) caramelises nicely golden brown. Use a fish needle or core temperature gauge to determine the correct cooking temperature. The fish fillets should fall off the bone without drying out. This is when the meat on the bone is about 53 °C.

Barbecue the flatfish bones with heads until they are nicely coloured and have a strong barbecue smell. Remove any overly burnt parts of the heads and place them in a saucepan with about 1 litre of water, so that they are just covered. Bring to the boil; as soon as the water boils, turn the heat down to low and leave to cook for 30 minutes. Strain the head and bones from the stock and, if necessary, reduce further until you have half a litre. Then, using a hand blender, add the butter and vinegar to form a slightly thick sauce. Season to taste with salt.

Cut the onions into slices of . cm. Melt 40 grams of butter (make sure it does not turn brown) and stew the sweet onion until it is glazy. Add the tarragon vinegar and season with salt. Keep in a saucepan to reheat later. Melt the remaining butter in a cast iron pan without allowing it to brown and stew the samphire and sea lavender over a low heat for a few minutes until al dente. Season with pepper, a pinch of salt and the zest of 1/2 a lemon.