Prepare the Mirepoix: Add the chopped carrots, onion, and celery to a food processor and pulse until very finely chopped.
Sauté the Vegetables: Heat a large Dutch oven or pot over medium-high heat and add olive oil and butter. Once the butter melts, add the finely chopped vegetables and cook for 3-5 minutes until softened and slightly translucent.
Add Garlic & Brown the Meat: Stir in the chopped garlic and cook for 1 minute until fragrant. Add the ground pork and beef, breaking them up with a spatula. Cook for 8-10 minutes until mostly browned.
Toast the Spices & Tomato Paste: Stir in the dried oregano and red pepper flakes, sautéing for 30 seconds. Add the tomato paste and cook for another 30 seconds to 1 minute, stirring, until it deepens in color and caramelizes slightly.
Deglaze with Milk & Wine: Make a well in the center of the pot and pour in the milk. Let it simmer and reduce for 3-5 minutes, stirring occasionally to prevent burning. Pour in the red wine and let it reduce for another 2-3 minutes.
Simmer the Sauce: Stir in the crushed tomatoes, and nestle in the Parmesan rind and bay leaves and season with salt. Bring the sauce to a gentle boil, then reduce to a low simmer. Cover partially with a lid, leaving a small opening.
Slow Cook: Simmer the bolognese for at least 1 hour, stirring occasionally. For the best flavor, let it cook for up to 3 hours, stirring to prevent sticking.
Cook the Pasta & Finish the Sauce: Cook the pasta according to package instructions, reserving about 1 cup of the starchy pasta water. Stir some of the sauce into the drained pasta, adding pasta water as needed to loosen the sauce.
Serve & Garnish: Plate the pasta and sauce, garnishing with freshly grated Parmesan cheese.