Cut off the radish leaves and wash. Reserve a few leaves for decoration, roughly chop the rest.
Leave the butter in a saucepan, add the diced shallot and the chopped radish leaves and sauté briefly. Then add the diced potatoes and the stock, put on the saucepan and simmer the soup for about 25 minutes. The potato should be soft.
Then puree everything finely with the mixer or hand blender. Bring back to the boil and stir in the crème fraîche. Finally, season and season to taste, beat with the mixer until frothy.
Cut the 3 radishes unpeeled into very thin slices and pour them over the soup with the leftover radish leaves.