Clean, wash and dice the fennel. Put the fennel greens aside as a garnish.
Heat the butter and sauté the finely diced onions in it until translucent. Then add the fennel, sweat briefly and deglaze with the broth. Simmer over a mild heat for about 20 minutes. Puree with a hand blender or in a blender, bring to the boil with the cream and season well with salt and pepper.
Serve on the plate with 1 tablespoon of crème fraîche and fennel greens.