Peel, wash and halve the potatoes and cook in boiling salted water for about 20 minutes. Clean and wash the Brussels sprouts and cook in boiling salted water for 10-15 minutes. Peel onion and celery. Clean and wash the leek. Cut prepared vegetables into fine cubes.
Heat the oil. Fry the meat for about 10 minutes, turning. Add vegetables after 5 minutes. Season with salt, pepper and sugar. Stir in tomato paste two minutes before the end of cooking time. Add tomatoes and bring to the boil. In the meantime warm up milk and butter. Drain potato water. Add milk butter to the potatoes and mash with a potato masher until mashed. Season to taste with salt and nutmeg.
In the meantime warm up milk and butter. Drain potato water. Add milk butter to the potatoes and mash with a potato masher until mashed. Season to taste with salt and nutmeg. Layer the mashed potatoes, sauce and Brussels sprouts in a greased casserole dish. Sprinkle with cheese. Bake in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for 20-30 minutes
Preparation time approx. 1 hour 20 minutes