For the potato soup, peel and dice potatoes and boil in 1 l salted water.
Sauté onion, garlic and parsley in 2 tablespoons butter. Add marjoram, mushrooms and bay leaf to boiling potatoes. Also add the onion mixture to the potatoes.
Melt 2 tablespoons of butter in a small saucepan, add flour and sauté briefly. Pour in the whipping cream to make a roux. Add the roux to the potatoes, stir well and simmer for 20 minutes until the potatoes break down a little.
Season the potato soup with vinegar, salt and pepper and serve with a dollop of sour cream.
Preparation Tip:
The best accompaniment to potato soup is good brown bread, which can also be baked in.