Defrost peas and possibly shrimps. Wash the potatoes and cook in boiling salted water for about 20 minutes. Drain potatoes, rinse with cold water and peel. Leave to cool.
Wash the dill, shake dry and chop finely, except for a little to garnish. Clean, wash and dice the cucumber.
Mix sour cream, yoghurt and horseradish. Season to taste with salt, pepper and sugar. Stir in dill. Quarter potatoes, put them in a bowl with cucumber and peas. Fold in horseradish cream.
Defrost prawns (see tip). Wash shrimps and pat dry. Peel garlic and crush it coarsely with a large knife. Heat oil in a pan. Fry the prawns and garlic over medium heat for 3-4 minutes while turning.
Season with a little salt and pepper.
Season the salad again. Arrange with prawns on plates and garnish with remaining dill.