Finely chop the onion. Cook the noodles in boiling salted water until they are firm to the bite.
Meanwhile, melt the butter in a larger saucepan, sprinkle the flour over it and sweat lightly. Deglaze with the water and bring to the boil. Add tomato paste, tomato ketchup and onions, simmer the sauce for a few minutes and carefully season with salt and sugar.
Drain the pasta and serve hot with the sauce!
Recommendation: Serve with either fried Vienna sausages, Bockwurst (sliced or in pieces) or Jägerschnitzel (fried, breaded hunting sausage).
Also possible with minced meat to taste (see Pasta Bolognese - child`s play).