Peel and wash the sweet potatoes and potatoes, cut into coarse pieces and cook covered in salted water for about 20 minutes.
Meanwhile peel and finely dice the onion and garlic. Heat 1 tablespoon of oil in a large frying pan. Fry the minced meat in it until crumbly. Fry the onion and garlic briefly. Season with salt and pepper. Add tomatoes together with juice and 150 ml water.
Crush the tomatoes coarsely, bring to the boil. Simmer covered for about 10 minutes.
Clean and wash the spring onions and cut them into rings. Add to the minced meat sauce and simmer for 2-3 minutes. Season the sauce with salt, pepper and sugar.
Preheat oven (electric cooker: 200°C/circulating air: 175°C/gas: level 3). Clean the chilli, cut lengthwise, remove seeds, wash and finely chop. Drain potatoes. Add milk, chilli and 3 tbsp. oil to the potatoes and mash everything to a puree.
Season with salt, pepper, cumin, vinegar and 1 pinch of sugar.
Put the puree into a greased casserole dish. Add the minced sauce. Crumble cheese and mix with sour cream. Spread on the casserole. Bake in the oven for 20-25 minutes.