Stir yoghurt and sour cream until smooth. Season to taste with salt, pepper and sugar. Peel onion. Chop onion and gherkins finely. Wash, quarter, core and finely dice 1 apple. Wash the dill and chop except for something to garnish. Stir everything into the yoghurt. Leave to stand for at least 30 minutes.
Rinse the maties, dab dry and cut in half lengthwise. Roll up the fillets and pin them with skewers. Wash 2 apples, cut into quarters, remove seeds. Cut quarters into about 20 thin slices. Sprinkle with lemon
Place one matie roll each on an apple wedge. Put a blob of yoghurt cream on each roll. Arrange on a plate with salad and radishes. Garnish with cranberries and remaining dill. Serve with pumpernickel taler with butter