Roughly dice the smoked fish and puree with the cutting stick of the hand mixer. Stir in crème fraîche and green pepper. Season to taste with some lemon juice and salt if necessary. Put it in a cold place
Boil the eggs for about 10 minutes. Quench and let them cool down. Peel onion and chop finely. Finely dice cucumbers and matie as well. Peel and chop the eggs and mix with onion, cucumber, matie and dill. Season with a little lemon juice and pepper. Cover and put in a cool place
Place the Rösti Taler unfrozen on a baking tray (possibly lined with baking paper). Bake in the preheated oven (electric cooker: 225 °C/recirculating air: 200 °C/ gas: level 4) for about 12 minutes. Spread the smoked fish mousse and matjes tartar on top and garnish