Clean, wash and halve the leek and cook in boiling salted water for about 15 minutes. Lift out of the water and drain well. In the meantime, wash and peel the potatoes and cook them in boiling salted water for about 20 minutes.
Peel and chop the onions and garlic. Heat the oil in a pan, crumble the minced meat, add and fry while turning. Add onions, oregano and garlic and fry for about 2 minutes.
Stir in tomato paste and then add tomatoes. Stir in ketchup. Season to taste with salt, pepper, paprika and sugar. Simmer at medium heat for about 5 minutes. Heat milk and fat.
Drain and mash the potatoes, add the milk little by little and mix in. Flavour with nutmeg. Layer the minced meat, leek (cut to length as desired) and puree in a greased ovenproof dish and bake in a preheated oven (electric cooker: 200 °C/ gas: level 3) for 15-18 minutes.
Serve garnished with marjoram as desired.