First peel the onion, cut into cubes and sauté. Then fry the ham cubes. Add the flour, extinguish with a little water, stir. Let thicken. Add the water in sips until the 1/2 liter is gone and the sauce has thickened. Then stir in a lot of mustard and the other ingredients as needed. Boil the eggs, peel them and add them to the finished sauce and let them get hot again.