For the eggs in mustard sauce, hard boil the eggs. For the mustard sauce, melt the butter in a saucepan, add the flour and stir in. Sauté lightly, do not brown.
Slowly pour in the soup, stirring vigorously to avoid lumps. Let the sauce simmer for another 3 minutes. Stir in the mustard and season with salt and pepper.
Peel the eggs, cut them in half and arrange them with the sauce on a plate. Serve with boiled potatoes.