Clean, peel and wash the kohlrabi, put some tender kohlrabi green aside. Cut the kohlrabi into slices about 1.5 cm thick, put 8 equal-sized slices aside. Finely dice the rest. Steam kohlrabi slices in 3/8 l boiling salted water for 8-10 minutes. Drain, catch the vegetable water and measure 200 ml
Peel and finely chop the onion. Heat 1 tablespoon of fat. Sauté half of the onion in it. Fry diced kohlrabi and rice. Add 1/2 l water, salt and bring to the boil. Cover and let it swell at low heat for about 20 minutes
Clean, wash and slice the tomatoes. Put kohlrabi slices in a flat greased casserole dish and season. Place 1 slice of ham, 1 slice of tomato and 1 slice of cheese on top. Bake in the preheated oven (electric cooker: 225 °C / fan oven: 200 °C / gas: level 4) for approx. 10 minutes
Finely dice the rest of the tomato. Heat 1 tablespoon of fat in a saucepan. Sauté the rest of the onion in it. Deglaze with vegetable water and bring to the boil. Stir in crème fraiche. Stir starch and 2 tbsp. water until smooth. thicken sauce with it, season to taste
Wash and finely chop the kohlrabigrün. Add to the rice with tomato cubes. Arrange everything, garnish if necessary