again. With a food processor or meat grinder, finely chop first the veal and beef, then the pancetta, onion, carrot and celery. Saute the pancetta and minced vegetables in the butter and oil in a heavy-bottomed casserole for 2 minutes over medium heat. Turn heat to very low, cover and continue cooking 30 minutes, stirring occasionally. Uncover the pot and raise heat to medium high. Add the beef, veal, mushrooms, salt and pepper. Cook, stirring constantly, until the meats just begin to lose their raw red color. Then pour on the wine and cook until it is entirely evaporated. Set a food mill with the medium blade over the pot and mill in the tomatoes. Stir everything together and simmer, covered for 40 minutes. If possible, complete preparation to this point several hours in advance, or even the night before you plan to use the sauce. Take it off the stove and let it cool if not serving immediately. Transfer to container. Cover and refrigerate. The sauce may also be made to this point and frozen. Shortly before serving time, bring the sauce slowly to a simmer. Simmer 5 minutes. Stir in the heavy cream and serve immediately over freshly cooked pasta, passing parmigiano and a pepper mill. To serve ragu in smaller quantities, heat about half cup of sauce per person and stir in 1.5 to 2 tablespoons cream per serving.