Heat olive oil in a large skillet over medium heat.
Add chopped onion, carrots, and celery to the skillet and cook, stirring occasionally, until vegetables are softened, about 5 minutes.
Add minced garlic and cook for 1 minute until fragrant.
Add ground beef and ground pork to the skillet. Cook, breaking up the meat with a spoon, until browned and no longer pink, about 7 minutes.
Transfer the cooked meat and vegetables to the slow cooker.
Pour the milk into the skillet and simmer over medium heat until it has mostly evaporated, about 5 minutes, scraping up any browned bits from the bottom.
Add the milk to the slow cooker.
Pour the white wine into the skillet and simmer until reduced by half, about 5 minutes.
Add the wine to the slow cooker along with crushed tomatoes, tomato paste, dried oregano, dried basil, salt, black pepper, red pepper flakes, and bay leaf.
Stir all ingredients in the slow cooker to combine.
Cover and cook on low for 6 hours, stirring occasionally if possible.
Remove the bay leaf and stir in chopped fresh parsley before serving.
Serve hot over cooked pasta of your choice.