In a large pan (or Dutch oven), over medium heat, sauté the onion, garlic, celery, and carrot in olive oil until tender and translucent. Add beef and sausage and cook until browned. Add tomato sauce, tomato paste, bay leaves, and basil. Add optional red pepper flakes. Simmer for about 45 minutes to 1 hour. When a dark, rich oil bubbles to the surface in a few spots, the sauce is done. Add salt and pepper to taste.