Dice the onion coarsely. Heat the oil in a saucepan and saute the onion until translucent. Pour in the broth, stir in pesto and creme fraiche, bring to a boil, reduce to a simmer and simmer 5 minutes.
Meanwhile, drain the tomatoes and chop.
Add the ravioli and tomato pieces to the broth and simmer 5 minutes over low heat. Season with salt and pepper. Serve garnished with basil leaves .