For this recipe I recommend the Krauselli noodles. The pasta is particularly suitable because it absorbs a lot of sauce.
Bring the pasta to a boil in cold, salted water. Chop the onion and melt butter in a small sauce pot and fry the onions until translucent. Then add the flour and make a roux.
Add as much water as desired amount of sauce is reached. Add half a tube of tomato paste so that the sauce is thick enough. Now season the sauce with 1 – 2 squirts of lemon juice, a little salt and sugar. Serve with the drained pasta.