Ingredients for the sauce:
Remove the bones from the fish and wash. Finely chop the onion, the white part of the leek and the celery and sweat over low heat until translucent. Add the fish bones, 1 piece of lemon and some lemon juice and fill with white wine and water. Salt and simmer slowly. When the stock boils, take it out of the oven and let it stand for about 20 minutes. Then pass the beer through a fine sieve and reduce slightly. Add the cream, add the 3 kinds of mustard and season with salt and sugar. Finally, tie with cornstarch.
Ingredients for french fries:
Peel the onions and finely chop them. Cut the boiled potatoes (preferably from the previous day) into slices. Heat the fat and fry the potato slices over a moderately high heat until they are nicely browned. Add onions and season with salt and pepper. If you like, you can also season with smoked salt or oil.
Ingredients for spinach:
Wash the spinach well. Peel an onion and garlic and chop finely. Sweat onion cubes and garlic in butter. Add the spinach and season with pepper, salt and nutmeg. Stir until the spinach has withered, adding some water if necessary.
Once washed and boned, dry, season with salt and lemon, and cover with flour to avoid sticking to the pan. Cook in fried fat over a moderately high heat until the fried side is slightly browned, then turn and bring to a boil.