For the cream of kohlrabi soup, first wash the parsley, dry well and pluck. Peel the onion and chop finely. Peel the kohlrabi and cut into small cubes.
Melt some butter in a pot and sauté the onions until translucent. Add the kohlrabi, fry well and dust with flour. Pour in the soup and simmer until the kohlrabi is soft. Lift out some of the kohlrabi and set aside as a chowder.
Puree remaining soup and blend with milk and sour cream (adjust amount if necessary, depending on desired consistency). Season to taste with salt and pepper. Add back in the kohlrabi cubes that were set aside.
Serve the cream of kohlrabi soup sprinkled with the chopped parsley.