For the celery puree, peel the celery and cut into large pieces. Then put in a saucepan, drizzle with a little lemon juice and fill up with the cream. Season with salt, pepper and nutmeg and slowly simmer until soft. As soon as the celery is soft, mix with the butter in a mixer to a creamy puree. If necessary, season again with salt and pepper and pass through a fine sieve.
For the sauce mignoette, sauté shallots and mushrooms in butter, deglaze with sherry and vinegar. Pour in white wine and Nolly Prat and reduce by about 1/3. Then add the mignoette pepper. Top everything up with the poultry stock, season with salt and sugar and reduce the liquid by about half. Strain the stock through a sieve and add butter and cream to a creamy, thick sauce using a blender. Finally, season again with salt, pepper and possibly a little lemon juice.
To season the turbot fillets, prepare a 10% salt solution (100g salt in 1 liter of water). Cut open the stonebut fillets with a butterfly cut (DO NOT cut through) and place between cling film so that they are about 2 mm thin. Then place the turbot fillets in the salt solution for about a minute. Then pat dry a little, place an egg yolk on top and close. Place the stonebut fillets in a buttered dish, lightly pepper and brush with melted butter. Then cover the mold tightly with cling film and place in the oven preheated to 80 ° C for about 20 minutes.
Coagulate the cleaned spinach in a little butter in a hot pan and season with salt, pepper and a little nutmeg.
Put some celery puree in the middle of a deep plate. Spread the spinach on top and put on the cooked stonebut fillet. Pour on the sauce and garnish with a few oven tomatoes if necessary.