Peel, wash and dice the kohlrabi. Peel and dice the onions.
Melt the butter in the pan, sauté the onion and kohlrabi cubes in it, deglaze with the broth, cook until soft.
In the meantime, wash the watercress and spin dry. Put a few leaves aside for the garnish, puree the rest in the cream with a mixer. Add the cream to the ready-cooked soup.
Season the soup to taste with salt, pepper, nutmeg and lemon juice. Garnish with watercress leaves.