For the meatballs, mix the minced meat in a bowl with the leek, mushrooms, thyme, tomato paste, egg and potato flour and shape into small balls. Place on a plate and cover and chill.
In the meantime, put the ingredients for the tomato sauce in a small saucepan, season to taste and bring to the boil. Let it thicken open for 10 minutes.
Heat the oil in a pan and fry the meatballs in portions until light brown. Place in a flat ovenproof dish and cover with the tomato sauce. Bake covered for 1 hour.
In the meantime, cook the pasta in salted water for 8-12 minutes until al dente. Quench and drain.
Divide the cooked noodles on preheated deep plates and top with the meatballs with sauce. Serve sprinkled with thyme.