Peel and cut Kohlrabi into about ½ inch cubes; boil in a little salted water (don't overcook). Do not discard the vegetable broth. 

Depending on how much Kohlrabi you have, make an Einbrenn (roux) with butter or oil and flour and cook to a light gold color. Then pour in enough of the vegetable broth and whisk to a creamy consistency.  Note:  For a richer, milder taste, you can also use milk or cream instead of the broth.  Combine with the Kohlrabi and simmer a bit.