Cook the rice in boiling salted water for about 20 minutes. Peel and halve the kohlrabis. Also cook in boiling salted water for about 15 minutes. Then hollow out the kohlrabi halves. Keep the inside.
For the sauce, peel and finely chop the onions. Heat the fat. Sauté onions and kohlrabi inside. Deglaze with stock and cream and cook for about 5 minutes. Wash the chervil and, except for a few leaves for garnishing, chop and stir in.
Puree with the cutting stick. Grate cheese and stir half into the sauce. Fill the kohlrabi halves with rice and place in an ovenproof dish. Spread the sauce in it and sprinkle with remaining cheese.
Bake in the preheated oven (electric oven: 200 °C/ gas: level 3) for approx. 30 minutes. In the meantime, wash, quarter and seed the tomatoes. Cut the fruit flesh into small cubes. Sprinkle kohlrabis with diced tomatoes and fresh chervil leaves before serving.