Wash potatoes thoroughly, boil in boiling water for 20-25 minutes. Quench potatoes, peel. Cut potatoes into slices. Coarsely crumble crispbread, grind in universal chopper. Roast mustard seeds covered in a pan without fat for 1-2 minutes until brown, remove. Peel onion, dice finely
Put the cucumbers in a sieve, let them drip off and collect approx. 100 ml stock. Add 2 tablespoons vinegar and 2 tablespoons oil and fill up to 175 ml with water. Add the onion, bring to the boil, pour over the potatoes, leave to stand for approx. 30 minutes, mixing gently 1-2 times. Wash the tomatoes, dab dry, halve or leave whole as desired. Cut the gherkins diagonally into slices. Wash the dill, shake dry, pluck the flags from the stalks and chop them, except for a little to garnish.
Cut the fish into pieces and puree. Mix the fish, egg, dill, 5 tbsp. ground crispbread and lemon juice well, season with salt and pepper. Form approx. 12 small meatballs from the mixture and turn them in the crispbread. Heat 2 tablespoons of oil in 2 frying pans, fry the meatballs for 6-8 minutes, turning them over at medium heat.
Fold tomatoes, cucumber, mustard seeds, sour cream and mayonnaise into the potatoes, season with salt, pepper, possibly vinegar and sugar. Arrange meatballs and potato salad on plates, garnish with dill