Peel kohlrabi like you peel apples. Remove leaves (don't throw away baby leaves, you can slice them and put into stew later) and cut kohlrabi like you cut potato for French fry potato, but just little bit thicker. Melt lard (or butter) in a pot, add flour and sauté it 1 minute. Add water and make creamy liquid. Add sliced kohlrabi and add water to cover the vegetable. Add salt and pepper and baby leaves if you want. Cook about 30 minutes or until kohlrabi softens. At the end add sour cream, stir well and serve.