For the radish-potato soup, peel, wash and dice the shallot.
Peel the potatoes, wash and cut into small pieces. Wash radishes thoroughly, cut off both ends and slice. Keep a few radish slices for decoration.
Heat the butter in a saucepan and sauté the onion cubes until translucent. Add the potatoes, sauté briefly, deglaze with the vegetable stock, add the bay leaf. Bring to the boil and simmer on low heat with the lid closed for 15 minutes. After this first simmering time, add the radishes and simmer in the same way for the next 5 minutes.
Remove the pot from the heat, remove the bay leaf and finely puree the soup. Stir in the crème fraîche, heat again very briefly and season strongly with sea salt, pepper and lemon juice.