Mustard Soup should never boil, otherwise it becomes sour. So that's why you put the heat of on time. If you let it cool you don't cover the whole pan with a lid the soup needs to breath when cooling down. This also helps to prevent it from becoming sour
You can use all kinds of mustard, but your soup looks extra nice if you use mustard with seeds.
Bake the flour for 5 minutes in the pan. If you don't do that the soup will taste after flour.
In spring smoked salmon with green asparagus are a real delicacy. If you want to make this dish in the winter you can use bacon with sliced leek as an alternative filling.
Use margarine instead of butter and leave out the sour cream. This recipe then becomes lactose-free.
Cut the smoked salmon into narrow strips and store until use in the refrigerator.
Melt the butter in a saucepan and add the flour.
Stir with a wooden spoon until a ball is formed.
Reduce heat to low and let the ball bake for 5 minutes.
Pour the cold vegetable stock, while stirring with a whisk, into the pan.
Let the soup boil for 10 minutes.
Lower the heat and add the mustard and season with salt and pepper.
Add the asparagus and simmer for 4 minutes.
Ladle the soup into a plate and divide the salmon among the plates.
Spoon into each plate a tablespoon sour cream. Serve immediately.