While the eggs are boiling, prepare a sear. Melt the butter and add the flour. Put some mustard in the finished stoving and let it brown for a moment. Gradually add the stock cubes dissolved in 500 to 600 ml of water to the baking oven until the sauce is as smooth as you want. Let the sauce continue to boil. Gradually add as much mustard until the desired flavor is achieved (in my experience that is about half a tube of mustard). Add salt and pepper to taste.
Peel the eggs and add them to the mustard sauce. Bring the whole thing to a boil again. And the age-old recipe is ready.