Peel the kohlrabis, cut off a lid. Hollow out the kohlrabi with a ball cutter and cook in boiling salted water for 15-20 minutes. Cut the kohlrabi lids and the flesh into small cubes.
Peel and finely chop the onion. Cut the smoked pork into small cubes. Coarsely grate the cheese. Heat the oil, fry the cubes of Kasseler lightly in it and take it out. Add fat and melt. Sauté the flour in it.
Deglaze with stock and milk and bring to the boil while stirring. Add kohlrabi cubes and 2/3 of the cheese and cook for about 5 minutes at low heat. Season with salt and pepper. Drain the kohlrabi.
Mix the cured pork and 1/3 of the sauce and fill into the kohlrabi. Pour the rest of the sauce into an ovenproof dish and put the kohlrabi into it. Sprinkle the rest of the cheese on top. Bake in a preheated oven (electric: 200 °C/ gas: level 3) for about 10 minutes.
Serve garnished with parsley.