Chop the Onion (1). Remove casings from the Italian Sausage (1 pound). Brush off and slice the Baby Bella Mushrooms (0.5 pound).
In a dutch oven, heat Olive Oil (1 tablespoon) over medium heat. Add the chopped onion and sauté for 3-4 minutes, until translucent. Add Italian sausage and Extra Lean Ground Beef (1 pound) and break meat apart using a wooden spoon or fork.
Cook until the meat is browned. Remove any excess fat from the browned meat and discard. Add Bay Leaf (2), Dried Basil (1 teaspoon), Dried Oregano (1 teaspoon), Crushed Red Pepper Flakes (1/4 teaspoon), and Marinara Sauce (4 cup). Stir to combine.
When the mixture starts to bubble, put the lid on the pot, slightly askew. Turn the heat down to a simmer. Let the sauce cook and thicken, about 45 minutes. Taste the sauce, and season with Salt (to taste) and Ground Black Pepper (to taste) as needed.
Add sliced baby bella mushrooms to the sauce, stir to combine. Replace the lid on the pot, and simmer for an additional 30 minutes. Serve over pasta, gnocchi, or spaghetti squash with freshly grated Parmesan Cheese (to taste).