Clean and wash the broccoli and cut it into small florets. Peel, wash and cut the stems into small pieces. Cook both in boiling salted water for 6-8 minutes. Peel and halve the onion and cut into thin slices.
Wash and halve the tomatoes and cut them into slices. Heat the oil. Sauté onion in it. Add tomatoes and steam for about 5 minutes while turning. Stir in tomato paste. Dust with flour and sauté.
Deglaze with 3/8 litres of water and carrot juice, bring to the boil and stir in the stock. Bring to the boil while stirring constantly and simmer for about 5 minutes. Season to taste with salt and pepper. Pour broccoli and tomato sauce into an ovenproof dish.
Rub cheese over it. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for 15-20 minutes.