Pour, in this order, the olive oil, the small onion, and the garlic. Mix a little.
Add the tomato paste and mix.
Add the heavy cream, and mix until it looks like in the next picture.
Seasoning. Put the all the seasons into a bowl and pour into the pan. And mix.
Pour the pasta into the pan, and the pasta water.
Put the butter on top.
On top, put the parmesan cheese. And mix.
If you want, serve topped with more basil and parmesan cheese. Done!