We like this piquant tomato sauce, which is easy on the calories, but if you are in the mood to indulge, try cream in place of the ricotta and yogurt. ~--------------------------------------------------------------------~-In a large saucepan, heat the oil and saute the onion and garlic until soft, about 5 minutes. Chop the tomatoes, reserving the liquid. Add the tomatoes, 1/2 cup of the reserved liquid, and the Tabasco sauce, basil, rosemary, and salt to the saucepan and mix well. Simmer, uncovered, for 30 minutes, adding more of the tomato liquid if the sauce is too thick. In a food processor or blender, process the ricotta cheese and yogurt until smooth. Stir the mixture into the tomato sauce and heat without allowing it to come to a boil. The sauce may look slightly grainy, but appears smooth when it is added to hot pasta. NOTE: Low-fat ricotta and yogurt can be used.