This is a variation on the classic Italian bolognese sauce. Adding dried porcini mushrooms gives a woodsy flavor. Porcini are sold at many supermarkets and at gourmet and natural foods shops.
Heat oil and butter in a heavy large pot over medium heat. Saute onions, garlic, carrot, and celery until tender and beginning to brown. Drain porcini, reserving soaking liquid. Add mushrooms, beef, and pork to mixture and cook, stirring regularly, until meat separates and is lightly browned. Add half-and-half and cook 5 minutes, stirring regularly. Add wine, reserved mushroom liquid, allspice, pepper, and salt; cook 7 minutes, stirring regularly. Add tomato sauce and tomatoes. Reduce heat to low and cook slowly, about 2 hours, stirring occasionally. Serve or freeze in plastic freezer bags.