Cornish brill with mushrooms, grapes, mussels and salsify

Begin by filleting the brill, so you can use the bones in the sauce. Remove the fillets and cut into 6 equal portions, ensuring you have 200g worth of trimmings leftover as well as the bones. You can ask your fishmonger to do this step for you. Reserve all the trimmings, bones and fillets in the fridge

To make the sauce, place a large pan over a high heat and add a dash of vegetable oil and the scallop skirts. Cook until the moisture has evaporated, then add the lobster head and cook until it turns ruby red. Add the butter and, once foaming, add the shallots, button mushrooms, fennel and peppercorns and cook for 5-8 minutes until soft

Deglaze the pan with the Armagnac and reduce to a syrup, then add the fish bones, half the mussels and the white wine and reduce to a syrup. Try not to stir the mixture too much as it can turn it cloudy. Once syrupy, add the chicken stock and simmer over a low heat for around 45–60 minutes, skimming the surface regularly

After this time, add the double cream, bring back to the boil then simmer for a further 10 minutes. Pass through a fine sieve into a clean pan. Briefly cook the remaining mussels until the shells just open, then pick them from their shells and reserve in the fridge

Peel 12 of the grapes for the garnish and season with sea salt. Dehydrate at 70ºC in a dehydrator, very low oven or even a hot airing cupboard for a few hours. The remaining grapes will be finely sliced and served raw as a garnish

To make the salt-baked celeriac, pick the leaves from the rosemary and thyme, place in a blender with the salt and blitz for 2 minutes. Transfer to a large stand mixer with the flour and egg whites and mix for 5 minutes. Add most of the water and mix for a further 10 minutes to create a salt dough – add the rest of the water only if it needs it. Transfer to the fridge to rest for 1 hour

After this time, preheat an oven to 200ºC/gas mark 6. Roll the salt dough out until 5mm thick then wrap it around the peeled celeriac, ensuring there are no holes. Place in the oven for 12 minutes, then reduce the heat to 175ºC/gas mark 4 and cook for a further 20 minutes. Check if it’s cooked by inserting a cocktail stick; if there is still resistance, continue cooking until just tender. Leave to rest for 12 minutes before breaking off the salt dough. Once cooled, finely slice the celeriac and use a cutter to stamp out neat circles

Next, return to the brill and make the mousse. Blend the 200g of brill trimmings with the egg white and salt until smooth then pass through a sieve. Beat in the double cream over ice, then season with salt and both peppers to taste

Slice the heads off the king oyster mushrooms and set aside. Very finely chop the stalks and place a frying pan over a high heat. Sweat the mushroom stalks down until caramelised to create a duxelle. Leave to cool completely then fold through the fish mousse and transfer to a piping bag

Finely slice the mushroom caps and layer onto 10cm squares of greaseproof paper, with each slice overlapping slightly. Pipe a 1cm layer of the mushroom mousse over the skin side of each brill fillet and turn over onto the sliced mushrooms. Place in the fridge until ready to cook

To make the celeriac and apple pureé, peel and dice the celeriac and apples and seal in a vacuum bag with a pinch of salt. Steam for 16 minutes or until tender. In the meantime, place the milk and cream in a pan and bring to the boil. Once soft, transfer the celeriac and apple to a blender and blitz, adding the cream mixture bit by bit until you have a smooth and creamy texture. If you don’t have sous vide equipment, simply simmer the celeriac and apple in the milk and cream until tender, then blitz, season and pass into a small pan ready to reheat

To prepare the salsify, peel the batons and rinse in cold water. Take a brand new sponge scourer soaked in clean cold water, then scrub the batons until perfectly round and even. Place them in a vacuum bag with the rest of the ingredients and steam at 86ºC for 18 minutes. Alternatively, simmer the salsify in the apple juice with the rest of the ingredients until tender. Portion into 6cm batons cut on the angle. When ready, reheat in a pan with a knob of butter

Now everything is ready, steam the brill at 62ºC for 12 minutes and reheat the sauce, adding in the mussels and herbs. Trim the sides of the fish so it’s beautifully square and plate up. Add neat spoons of the pureé, the salsify baton, dehydrated grapes and celeriac sheets, then finish with sliced grapes, dill and sea purslane with the sauce served on the side