Place spinach in a sieve and allow to defrost at room temperature. For the roux, melt 3 tablespoons of fat. Stir in flour and sweat briefly. Remove the pot from the heat.
Peel onions and celery. Dice 1 onion and celery. Clean the leek, cut into rings and wash. Melt 1 tablespoon of fat in a pot. Add onion, celery and leek and fry over medium heat for about 5 minutes while turning.
Douse with white wine, fill up with fish stock and bring to the boil. Wash basil, shake dry, put 1 stalk aside for garnishing. Add remaining basil and star anise to the fish stock and simmer for about 30 minutes.
Wash the fish, dab dry, season with salt and pepper and turn in a little flour. Cut 1 onion into cubes. Melt 1 tablespoon of fat, fry onion until translucent, peel garlic, press it through a press and add it.
Stir in the spinach and stew for about 10 minutes. Season to taste with salt, pepper and nutmeg. Heat clarified butter and fry fish for 10-12 minutes, turning once. Pour the sauce stock through a sieve and collect it.
Quickly pour into the pot with the roux and stir. Bring to the boil and simmer for 2-3 minutes, stirring continuously. Season with salt and pepper and refine with cognac and cream.
Arrange spinach, fish and sauce on plates and garnish with remaining basil and star anise.