Thaw the plaice fillets on kitchen paper. Wash the fillets, dab dry, cut in half lengthwise and sprinkle with 2 tablespoons of lemon juice. Season with salt. Halve the salmon slices, place on the fillets and spread with horseradish.
Roll up and fix with wooden sticks. Bring 500 ml water, wine, 2 tablespoons of lemon juice, salt and peppercorns to the boil. Put the plaice rolls in and let them simmer for 10 minutes. Meanwhile boil 375 ml water and 1/2 teaspoon salt.
Pull the pot off the stove. Add cold milk and fat. Stir in mashed potato powder with a wooden spoon and let it swell for about 1 minute. Pour the mashed potatoes into a piping bag with star-shaped spout and squirt a spiral onto a plate.
Drizzle with pesto. Lift the plaice rolls out of the stock, let them drip off a little and arrange around the puree. Garnish with lemon slices, chilli and dill.