Wash, peel and quarter the potatoes. Cook in boiling salted water for about 20 minutes. In the meantime, clean, peel, wash and cut the soup greens into medium sized pieces. Peel and finely chop the onion.
Heat the oil in a pot. Brown the onion and soup vegetables in it. Add minced meat and fry for about 5 minutes. Stir in tomato paste and flour, sweat briefly. Add tomatoes with juice and simmer for about 10 minutes.
Season with salt, pepper and oregano. Drain the potatoes and let them steam briefly. Boil up milk and fat. Mash potatoes, stir in milk and fat mixture. Season with salt and nutmeg. Put Bolognese into an ovenproof dish (approx. 30x18 cm; 1 litre capacity).
Spread mashed potatoes on top. Grate the cheese roughly and sprinkle the mashed potatoes with it. Bake in the preheated oven (electric cooker: 225 ° C/ no air: 200 °C/ gas: level 4) for about 10 minutes.