Crisp up the pancetta. Melt the butter and olive oil in a dutch oven over medium low heat. Add the pancetta, and cook while occasionally stirring, until crispy. This process takes about 10-12 minutes, don't rush. Use a slotted spoon to remove the pancetta from the pot and transfer to a small bowl.
Finely mince the veggies. While the pancetta cooks, Add all the veggies and garlic to the bowl of a food processor and pulse until everything is finely minced. This saves tons of time!
Cook the beef and sausage. Add the ground beef and Italian sausage to the pot and keep the heat low. Cook while stirring often until the meat is cooked through and really finely broken up. Don't brown the meat, just cook low and slow until it's cooked through.
Add the veggies. Increase the heat to medium and add the finely chopped veggies to the pot. Cook for 6-8 minutes, stirring occasionally, until the veggies are soft. Add the tomato paste to the pot and really mix it in. Cook until it's darkened in color, about 5 minutes.
Add the remaining ingredients. Add the wine to the pot and use it to help scrape up any brown bits on the bottom of the pan. Add the milk, tomatoes, bay leaves, crispy pancetta, and parmesan rind to the pot. Season with salt and pepper and reduce the heat to low. Cover the pot.
Simmer. Simmer on low for 2 1/2 – 3 hours, stirring every hour or so. The sauce should be thick and deep red in color. Season to taste with salt and pepper and remove the bay leaves. You can store the sauce in an airtight container up to 1 week after it's cooled to room temperature.