Clean the kohlrabi, potatoes, onion and garlic and cut into cubes.
Sweat the onion and garlic in butter. Add the kohlrabi and potatoes. Season with salt and pepper. Steam for three minutes. Then deglaze with broth. Simmer for 10 minutes with the lid on. Then remove the lid and let it simmer a little. Whip the cream until it is half stiff, fold in the rosemary and add both to the vegetables. Let it boil again. Finally fold in the parmesan.