Onions and mushrooms are finely chopped and sauté until soft with half butter. Add ketchup and parsley mixture stew again and then add the egg yolks, stirring until boiling. After cooling slightly beaten whites, pepper, and stir. Baguette cut into slices 2 cm thick, smeared with the remaining butter, cover with prepared mixture and sprinkle with grated cheese. Bake briefly in a hot oven with overhead heating or BBQ and served warm.