Peel rutabaga, carrots and potatoes and cut them into small pieces. Cook in boiling salted water for about 20 minutes. Peel onions and garlic and chop finely. Wash oregano, shake dry, pluck leaves from the stalks and chop, except for something to garnish. Heat the oil in a pan.
Fry the chopped oregano for about 10 minutes while turning. Add onions and garlic after about 5 minutes. Add the tomatoes and chop them with a spatula. Bring sauce to the boil, season with oregano, salt, pepper and sugar. For the béchamel sauce, melt the fat in a saucepan. Add flour, stir and sweat for 2-3 minutes while stirring. Add milk and stock while stirring. Bring to the boil and simmer for about 5 minutes while stirring. Drain the vegetables and mash them with a potato masher to a pulp. Alternately layer potato and vegetable masher and meat sauce in a greased casserole dish.
Add milk and stock while stirring. Bring to the boil and simmer for about 5 minutes while stirring. Drain the vegetables and mash them with a potato masher to a pulp. Alternately layer potato and vegetable masher and meat sauce in a greased casserole dish. Finish with béchamel sauce and sprinkle with cheese. Bake in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 30 minutes. Sprinkle with remaining oregano leaves
Preparation time approx. 1 hour 20 minutes