Heat the spinach with 100 ml water in a saucepan over medium heat covered for about 16 minutes. Stir several times. Rinse the fish and dab dry with kitchen paper, cut in half lengthwise.
Wash the dill, dab dry and chop coarsely. Season fillets with salt and pepper and sprinkle with the dill. Roll them up and stick them together with wooden skewers. Bring lemon juice, wine and 150 ml water to the boil with salt and peppercorns, place the rolls in it.
Leave to stand at low heat for about 8 minutes. Peel and finely chop the onion. Remove the rolls and keep warm. Pour the fish stock through a sieve, catch the stock. Heat the lobster paste in a pot and sauté the onion.
Add cream and stock while stirring, simmer for 5 minutes at low heat. Bring spinach to the boil briefly, season with salt and pepper if necessary. Stir the prawns, except for 2 tablespoons, into the sauce.
Season to taste with salt and pepper. Serve the plaice rolls with sauce and spinach. Sprinkle the rest of the prawns on top.