Mix flour, fat, 1 egg, 1/2 teaspoon salt and 2-3 tablespoons cold water to a smooth dough. Chill for 30 minutes. In the meantime, clean, wash and cut the leek into pieces. Blanch briefly in boiling salted water. Sprinkle prawns with lemon juice. Coarsely grate cheese. Mix remaining eggs, sour cream and 2/3 of the cheese.
Season with salt, pepper and nutmeg. Roll out the dough to the size of the mould and press the rim firmly. Fill leek and crabs into the form. Pour egg milk over it. Sprinkle with sesame seeds. Bake in the preheated oven (electric oven: 200 °C/ gas: level 3) for 45-50 minutes. Garnish leek-crab quiche with dill and serve