Peel onion and chop very finely. Wash and drain the radish sprouts. Wash chives, dab dry and cut into small rolls. Wash parsley, dab dry and chop finely. Wash, quarter, seed and dice the tomato.
Mix quark and crème fraîche, season with salt and pepper. Stir 3/4 of the chives, 3/4 of the sprouts, 3/4 of the onions, 3/4 of the parsley and 3/4 of the tomato into the quark. Spread bread with fat, cut in half and spread with quark. Serve one half of the bread on a small plate with the remaining chives, parsley, onions, sprouts and the remaining diced tomatoes, sprinkled with a lettuce leaf and parsley as desired