Wash the salmon, dab dry and cut into cubes. Finely puree with egg yolk and cream in the universal chopper. Season with salt, pepper and lemon juice. Wash the plaice fillets, dab dry, spread with 1/8 of the salmon mixture and roll up.
Peel and finely chop the onion. Spread a flat roasting pan with butter. Dice the onion and pour on wine. Season with salt and pepper. Bring to the boil, remove from the stove. Put rolls into the roaster and cook in the preheated oven (electric cooker: 125 °C/ convection oven: 100 °C/ gas: not suitable) for about 15 minutes.
For the vinaigrette, whisk vinegar, salt, pepper and honey. Embezzle oil. Clean, wash and halve the tomatoes. Wash spinach, shake dry. Mix spinach and tomatoes. For the caper butter, drain capers well and chop them.
Melt butter and stir in capers. Arrange rolls and salad on plates. Drizzle salad with vinaigrette and roulades with caper butter.