Peel the potatoes and cut into slices. Rinse off the leek, clean and cut diagonally into approx. 1 cm thick rings. Sauté in 1 tablespoon of oil until firm to the bite and then allow to cool.
Peel the onion and garlic, dice finely and sweat in 2 tablespoons of heated oil until golden. Add the minced meat, fry until crumbly and season with oregano, salt and pepper. Add tomato paste and chopped tomatoes, let everything reduce a little. Whisk the sour cream with the cream, season well with salt and pepper.
Preheat the oven to 180 ° C top / bottom heat (convection: 160 ° C). Grease a baking dish.
Fill the leek rings into the baking dish and distribute the minced meat mixture on top. Layer the potato slices on top like a roof tile. Pour the sour cream over the lasagne, sprinkle with the cheese and bake in the oven for about 45 minutes.