Wash the potatoes and cook in plenty of boiling water for about 20 minutes. Rinse briefly under cold water, drain, peel while still hot and cut into slices. Let cool off
Peel and finely chop the onion. Clean and wash the cucumber and cut or slice it thinly. Mix vinegar, broth and mustard, season with salt, pepper and sugar, fold in 5 tablespoons of oil. Fold the cucumber, vinaigrette and onion into the potatoes and leave to marinate
Clean and wash spring onions, first cut into fine rings, then chop. Wash the dill, shake dry. Pluck the flags from the stems and chop them, except for something to garnish. Cut fish into cubes. Finely chop 2/3 of the fish in the universal chopper. Knead mashed and diced fish, spring onions, egg, breadcrumbs and chopped dill. Season with 1 level teaspoon of salt, pepper, lemon zest and juice
Form 8 oval meatballs from the mixture. Heat 1 tablespoon of oil in 2 pans. Fry the meatballs for 8-10 minutes. Season the salad with salt, pepper and sugar again, arrange the meatballs in portions on plates and garnish with dill.