Wash the plaice fillets, dab dry and sprinkle with lemon juice. Sprinkle with salt and pepper, roll up and pin with wooden skewers. Wash, peel and finely grate the horseradish. Cut the rind off the white bread. Crumble the white bread finely.
Peel onion and chop finely. Melt 20 g butter. Sauté onion in it. Add half of the white bread. Deglaze with the milk while stirring. Stir in horseradish. Season to taste with stock, salt and pepper. Put 3 plaice rolls into 4 small moulds. Pour horseradish sauce over them. Sprinkle the remaining breadcrumbs over it.
Season to taste with stock, salt and pepper. Put 3 plaice rolls into 4 small moulds. Pour horseradish sauce over them. Sprinkle the remaining breadcrumbs over it. Spread 30 g butter in small flakes on top. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for 15 minutes. Serve garnished with dill, lemon and grated horseradish