Put the tortellini in a baking dish. Fry the onions and minced meat in a saucepan. Quarter and core the tomatoes. Add to the minced meat and fry briefly. Deglaze with cream and stock, bring to the boil and refine with creme fraîche. Cut the basil into strips and add to the sauce. Season with salt and pepper and season with oregano and thyme if necessary. Pour the sauce over the tortellini, sprinkle with cheese and bake at 180 ° C (top and bottom heat 200 ° C) for about 30 minutes.