Peel the kohlrabi and cut into small pieces. Finely chop the thyme.
Heat the butter in a saucepan, add the kohlrabi pieces and the thyme and sauté. Fill the pot with 500 ml of water. Season to taste with salt, pepper and the broth. Let it simmer for about 15 minutes.
Puree the soup with the hand blender, add the cream and let everything simmer briefly. Serve the soup warm.