1. Cook the pasta in a slightly salted water for 7-8 min. Drain and add butter or 1-2 tbs. olive oil (optional).

  2. In the meantime heat the olive oil over a medium-low heat.

  3. Add the pesto, the onion and a pinch of salt and pepper.

  4. Fry for 5 min (until the onion softens).

  5. In a large bowl add the mixture to the spaghetti and sprinkle with the parmesan. If you wish, you could add some basil leaves on top.