Cut the John Dory fillets straight down the centre so you have 8 pieces, then score the centre of each piece

Chop the bones, remove the gills from the head and wash the bones and head under running water for 20 minutes. Drain and set aside

Place 100g of the butter into a pan and melt gently. Sweat down the shallots, garlic and celery until soft but not coloured. Add the bones and sweat for a couple of minutes

Add 200ml of the cider and enough water just to cover the bones. Bring to the boil and cook very slowly for 15 minutes

Strain through a sieve lined with a muslin cloth into a pan. Reduce the stock over a medium high heat to 250ml. Add the double cream, re-boil and set to one side

Cut the celeriac into 5mm dice and cook in boiling salted water. Refresh in iced water then drain and set to one side

Heat a pan with a lid and add the cleaned mussels. Pour in the remaining cider and cover with the lid so that the mussels steam open very quickly

When the shells have opened, tip them into a colander set in a bowl to retain the liquid

Remove the mussels from the shells and put to one side. Pass the liquid through a sieve lined with six layers of muslin cloth and set aside

To cook the fish, get a large non-stick pan and add the olive oil. Place the fish into the hot oil skin side down and pan fry gently until half cooked

Turn the fish over and remove the pan from the stove, the fish will cook through in the residual heat

Wilt the spinach in the rest of the butter and season with salt

Bring the sauce up to the boil and add some of the mussel stock to taste. Add the celeriac, apple and mussels, bring back to the boil then add the chives

Divide the spinach between four bowls, arranging it in mounds in the centre of each bowl

Pour the sauce around and arrange the apple, celeriac and mussels around the bowls

Place two fillets of John Dory per portion on the spinach and serve immediately