Cut the onion into small pieces and sweat in about 20 g butter until translucent. Scald the tomatoes briefly, peel off the skin, quarter the tomatoes and add to the onions. Bring to the boil and deglaze with the wine. Let it boil down until almost all of the liquid has evaporated, then pass through a fine sieve.
Top up with broth and Cremefine and cook for a few minutes. Season to taste with pepper and salt. Mix the remaining ice-cold butter in small pieces into the simmering soup. That gives a velvety bond. At the end, mix in the basil cut into fine strips.