Clean the cauliflower and broccoli, wash them and cut them into small florets. Cook in boiling salted water for about 10 minutes. Then drain and store 300 ml of vegetable water. In the meantime clean, wash, quarter and seed the tomatoes.
Cut the fruit flesh into small cubes. Grate cheese finely. Peel and chop onion. Heat the fat and fry the onion until transparent. Add flour and sauté. Add vegetable water and cream while stirring constantly and bring to the boil.
Season to taste with salt, pepper and nutmeg. Fill cauliflower, broccoli and tomato cubes into an ovenproof dish. Pour sauce over it. Sprinkle with cheese and bake in a preheated oven (electric cooker: 200 °C/ gas: level 3) for about 15 minutes.