Sauté the onions and pressed garlic clove in the melted butter. Add the peeled and chopped potatoes and sauté briefly. Pour the cream and meat stock and cook for 15-20 minutes (until the potatoes are soft), season with salt and pepper. Add watercress to the soup. Now puree everything with a hand blender.
If the soup is still too thick, dilute it with a little milk. Serve hot.
Tip: The watercress can be replaced with parsley or chives as needed.