Melt the butter in a saucepan and use the flour to make a light brown roux. Remove the pot from the oven. Slowly stir in the meat or vegetable stock. Now put it back on the stove and stir carefully with the whisk
cook until the sauce is thick. Simmer for about 10 minutes, stirring frequently, so that the flour taste disappears. Add the mustard and stir in well. Season to taste with nutmeg, salt and pepper.
Cut the eggs into slices and add to the sauce. Stir gently so that some of the yolks combine with the sauce. Add freshly chopped parsley.
Go well with it: floury boiling boiled potatoes and mouse-ear lettuce (Rapunzel) which is dressed with garlic and diced bacon.