Clean the fennel and cut into smaller pieces. Peel and dice the potato. Finely chop the shallot. Crush the fennel seeds in a mortar.
Sauté vegetables and fennel seeds in olive oil for 5 minutes. Pour in the stock and simmer for 20 minutes until the vegetables are soft. Mix with a hand blender and, if necessary, pass through a sieve. Add the crème fraîche and mix again. Season with pepper and garnish with a little fennel green.