1 Loosen the trout fillets from the skin and cut into 3 cm (approximately 1-inch) pieces.
2 Rinse celery, wipe dry and remove any strings. Cut the bell pepper in half, remove seeds, rinse and dry. Peel cucumber, halve lengthwise and remove seeds.
3 Cut all vegetables into small cubes and place in a bowl.
4 Rinse dill, shake dry, pluck leaves and reserve some for garnish.
5 Combine the trout and vegetables in a bowl, then fold in the dill.
6 Fold in the sour cream and season with salt and pepper.
7 Spread the pumpernickel thinly with butter and spread the trout tartare on top, dividing evenly. Sprinkle with reserved dill and serve.