In a large skillet, heat the olive oil over medium heat. Add the diced onion, garlic, carrot, and celery. Sauté for about 5 minutes until the vegetables are softened.
Add the ground beef and ground pork to the skillet. Cook until browned, breaking it up with a spoon, about 8-10 minutes. Drain any excess fat.
Transfer the meat mixture to a slow cooker. Stir in the crushed tomatoes, tomato sauce, tomato paste, oregano, basil, sugar, salt, pepper, bay leaf, and red wine if using.
Cover and cook on low for 6-8 hours or on high for 3-4 hours, stirring occasionally.
Before serving, remove the bay leaf and taste the sauce. Adjust seasoning if necessary. Serve over your favorite pasta and garnish with fresh basil if desired.