Finely puree trout fillets, crème fraîche and horseradish with the chopping stick of the hand mixer. Whip the cream until stiff and fold into the trout mousse. Roast the bread and use a round cookie cutter (4 cm Ø) to cut 2 circles from each slice of bread.
Pour the trout mousse into a piping bag with a star-shaped spout and squirt onto the bread. Wash the lettuce leaves, drain and pluck into bite-sized pieces. Wash and quarter the tomatoes. Arrange frisée, bread and tomato quarters on a plate.
Wash the dill, cut finely and sprinkle over the top.