Bring a pot of water to a boil. Put the eggs in and cook the eggs for 7-8 minutes on medium heat (If you want them completely hard-boiled, cook them for 10 minutes). When the eggs are done boiling, pour them over with cold water to stop the cooking.
While the eggs are boiling, cut the bacon into cubes, and fry crispy on a frying pan over medium heat.
At the same time, melt the butter in a saucepan. When the butter has melted, whisk the flour in and cook for 1 minute before adding the milk. Then add milk a little at a time while still whisking in the sauce.
When all the milk has been added, add the mustard, sugar, salt and pepper to the sauce.
If the sauce is too thick, there can be added a little more milk. Finally taste the sauce with more mustard, salt, pepper, and sugar if necessary.
The cooked eggs are peeled and divided lengthwise, and placed in the hot mustard sauce. Sprinkle with cress and crispy bacon, and serve with rye bread.