Drain the capers. Dab maties dry. Peel onion. Wash tomatoes and apple. Quarter apple and remove core. Cut matie, onion, tomatoes and apple into fine cubes. Chop capers coarsely if necessary.
Mix all ingredients.
Mix yoghurt and sour cream. Season with salt, pepper, some sugar and lemon juice.
Wash the salad leaves and drain well. Spread bread with butter and cut in half. Distribute lettuce leaves on plates. Arrange the matjes tartar on top, e.g. with the help of hors d'oeuvre rings. Drizzle yoghurt sauce over it.
Add bread.