Defrost the mussels in advance in the lower compartment of the refrigerator. Pour a glass of cold water into a saucepan, put the mussels, bring to a boil and remove from heat.
Strain the resulting broth through a sieve. Put the mussels in a bowl, cover and set aside.
Peel the potatoes, cut into small cubes and boil for 10 minutes in a small amount of water.
Dry.
Add to the mussels.
Peel and finely chop the onion, cut the bacon into strips. In a saucepan, heat the butter, fry the bacon for 3 minutes, add the onion and fry for another 5 minutes.
Add flour and mix thoroughly.
And cook, continuing to stir, for another 4 minutes.
Heat the milk without bringing it to a boil. Pour warm milk, a glass of hot water and mussel broth into a saucepan. Boil for 5 minutes.
Add potatoes and mussels. Cook for 4 minutes, remove from heat.
Wash the parsley and finely chop. Season the soup with cream, put parsley, salt and pepper to taste, then cook for another half a minute.