In a Dutch oven or large heavy-duty saucepan/skillet, cook the beef and sausage over medium heat until no longer pink. Drain all but 2 tablespoons of the grease and add the onion and garlic. Cook, stirring often, for 5 minutes or until veggies are soft and fragrant.
Add the crushed tomatoes (or thawed tomatoes, if using frozen), marinara, tomato paste, Italian seasoning, fennel seeds, Bay leaves, sugar, salt and pepper. Mix well and increase to medium-high heat. Bring to a boil and then reduce to a simmer.
Simmer uncovered for 2-3 hours, stirring occasionally to avoid scorching on the bottom of the pan. Remove Bay leaves and allow sauce to cool before pouring into quart-size mason jars. Store in the refrigerator for up to 1 week. If freezing, store in airtight containers or sealable bags for up to 6 months.