Cook the spaghetti in salted water according to the instructions on the packet. Peel and finely chop the onions, sweat in the melted butter until translucent. Mix until foamy with a hand blender.
Add the cream, oregano, salt and plenty of freshly ground black pepper. Let simmer for five minutes.
Mix the sauce and pasta together and serve sprinkled with plenty of freshly grated Parmesan (or Grana Padano). I recommend red wine with it.