Peel onion and garlic and cut into fine cubes. Heat the oil. Fry the minced meat for about 10 minutes while turning it. After 6 minutes add onion and garlic. Stir in tomato paste and dust with 1 tbsp. flour.
Add 250 ml stock and 250 ml water, bring to the boil while stirring. Wash thyme, oregano and basil, shake dry and, except for a little garnish, pluck leaves from the stalks and chop.
Season the sauce with herbs, salt, pepper and sugar. For the béchamel sauce, melt the fat in a saucepan, add 3 tbsp. flour and sauté. Deglaze with 250 ml broth and milk. Bring to the boil, simmer for about 5 minutes.
Season with salt, pepper and 1 pinch of nutmeg. Wash, clean and slice the tomatoes. Grease an oven dish (approx. 17 x 28 cm). Spread some béchamel sauce thinly on the bottom of the dish.
Place 3 lasagne plates on top. Spread half of the mince on top. Place 1/3 of the tomato slices on top, spread with béchamel sauce and cover with 3 lasagne sheets. Repeat the process and finish with a layer of lasagne sheets and the rest of the sauce.
Spread the rest of the tomatoes on the lasagne. Grate the cheese and sprinkle over the lasagne. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 45 minutes until golden brown. Arrange in portions and garnish with the remaining herbs.