Spread elongated terrine mold with softened butter and place in refrigerator.
Roughly dice salmon and trout fillets, mix, sprinkle with juice of one lemon and put in refrigerator for 1 hour.
Then chop fish cubes with the cutting staff of the blender (or in the hand mixer). Work the egg into the fish puree at the beginning, then the crème fraîche and whipped cream. Season the farce with salt, season with pepper and spread into the precooled give. Give the give several hearty pokes on the surface so that no air bubbles form in the farce.
Place the juice pan in the oven on the 2nd rack from the bottom and fill with boiling water. seal the give and place in the water. Cook the terrine in the heated oven (gas 2-3, convection oven 190 °C) for 30-35 minutes. Turn off the heat, let the terrine stand for 10-15 minutes, remove from the water bath and cool for 2-3 hours.
Turn out terrine from the mold onto a board. give clean and spread without folds with cling film. Scrape the leaked fat from the terrine. Slide terrine repeatedly into mold.
Place the remaining smoked salmon on top. Place the lid on the mold. Set the terrine aside to cool for one night.
A day later, invert the terrine, remove the foil. Cut the terrine into slices with an electric kitchen knife or possibly a serrated knife and garnish with freshly shaved horseradish and a small lettuce (cocktail tomato, tomato sauce, etc.).