Cook the pasta in boiling salted water according to the instructions on the packet. Separate 3 slices of sausage thinly, quarter the remaining sausage lengthwise and cut into slices. Quarter peppers, clean, wash and cut into strips.
Wash, clean and slice the tomatoes. Peel onion and cut into fine cubes. Heat 1 tablespoon of oil. Sauté the onion briefly. Add tomato paste and sweat for about 5 minutes.
After 3 minutes dust with 1 tablespoon of flour. Deglaze with 200 ml vegetable stock. Bring to the boil and simmer at low heat for about 5 minutes. Season with salt, pepper, paprika and sugar. In the meantime heat up fat in a pot, dust with 35 g flour, sweat and gradually add 300 ml broth and milk.
Boil up while stirring. Season with salt, pepper and nutmeg. Heat 1 tablespoon of oil, fry sausage for about 5 minutes while turning. After 3 minutes add paprika. Wash thyme, shake dry, except for a little to garnish, pluck leaves from the stalks.
Stir the prepared tomato sauce and thyme into the sausage-vegetable mixture. Grease a casserole dish. Spread a little béchamel sauce thinly on the bottom. Place 1/3 of the pasta on top of it, side by side. Add half of the sausage-vegetable mixture, half of the tomato slices, 1/3 of the sauce and mix well.
Layer the rest in the same way, leaving 3 tomato slices and pour the last noodles with the remaining sauce and sprinkle with cheese. Spread the remaining tomato slices and sausage slices on top. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for 25-30 minutes.
Garnish with thyme.