For the tomato cream sauce, heat the butter in a pan. Sauté the chopped onion until translucent, add the tomato pieces and cook for 3 minutes.
Deglaze with whipping cream, cover and simmer for another 5 minutes. Then remove the lid and let the whipped cream simmer down a bit.
Stir in tomato paste and season the tomato cream sauce with salt, pepper and basil.