This rich and homey meat sauce is the ultimate winter comfort food. Our spin is worth making it again and again.
In a 4-quart Dutch oven or deep skillet heat butter and olive oil over medium-high heat. Add pancetta; cook and stir until just starting to brown, about 8 minutes, stirring occasionally. Reduce heat to medium. Add onion. Cook and stir until translucent, about 5 minutes. Add carrot and fennel. Cook 2 minutes more.
Add the beef and pork to the Dutch oven. Season with salt and pepper. Using a fork, break up the meat (you want to retain some larger pieces for texture). Cook until browned. Add the wine. Using a wooden spoon, scrape up the browned bits from the bottom of the pan. Simmer, uncovered, until the wine has evaporated, about 40 minutes.
Add the milk and nutmeg. Simmer, uncovered, until the milk has evaporated, about 20 minutes, stirring frequently. Once the milk has evaporated, add the tomatoes; stir to combine. When the tomatoes just start to bubble, reduce heat to low and add the Parmesan rind. Cook, uncovered, 2 1/2 to 3 hours, stirring occasionally. As the sauce cooks, liquid will evaporate and the sauce will start to look dry. Add 1/2 cup water at a time (2 to 3 cups water total) and continue to simmer as liquid evaporates. Serve over hot cooked pasta.
Transfer mixture to an airtight storage container. Cover and chill up to 3 days or freeze up to 3 months.
Save the fennel bulb for another use.