For the plaice fillet rolls, clean plaice fillets, season with salt, pepper and lemon juice and spread with mustard and horseradish.
Cut gherkins into strips, finely chop onions and place on top of fillets. Roll up fish and close with a toothpick. Place in a perforated steamer basket.
Place fish stock, white wine and dill in an unperforated steamer basket.
Knead butter and flour, form small balls and place in stock.
Cook fish and stock in parallel (at 85°C for 6-8 minutes). Stir after cooking to allow flour balls to dissolve and thicken sauce.
Fold in heavy cream and season with salt, pepper and white wine.