Boil the egg in boiling water for about 7 minutes until soft. Wash, clean and seed the tomatoes. Cut the flesh into small cubes. Wash chives, dab dry and cut into fine rolls, put something aside for sprinkling.
Wash, clean and slice the radishes. Quench egg cold. Mix quark with tomatoes and chives, season with salt and pepper. Spread the quark on the onions. Cover with radishes and sprinkle with chives and pepper.
Add the egg.