Creating this delightful Mac and Cheese Meatloaf Casserole requires a few straightforward steps. Follow this guide to achieve a delicious outcome:

1. Preheat Oven: Begin by preheating your oven to 350°F (175°C).
2. Prepare the Meatloaf Mixture: In a large bowl, combine ground beef, breadcrumbs, egg, chopped onion, minced garlic, Italian seasoning, salt, and black pepper. Mix until well combined.
3. Prepare the Mac and Cheese Layer: In a separate bowl, mix the cooked macaroni pasta, 1 cup of shredded cheddar cheese, milk, and mustard (if using). Stir until evenly distributed.
4. Combine Layers: In a greased casserole dish, press half of the meatloaf mixture into the bottom to create an even layer. Then, spread the mac and cheese mixture on top of the meatloaf layer.
5. Add Remaining Meatloaf: Top the mac and cheese with the remaining meatloaf mixture, sealing it gently.
6. Spread Marinara Sauce: Pour marinara sauce over the top layer of the meatloaf. This adds flavor and moisture as it bakes.
7. Add Cheese: Sprinkle the remaining 1 cup of shredded cheddar cheese on top of the marinara sauce.
8. Bake: Place your casserole in the preheated oven and bake for 45-50 minutes, until the meat is cooked through and the cheese is melted and bubbly.
9. Rest: Once cooked, allow the casserole to cool for 5-10 minutes before serving. This helps it set and makes it easier to slice.
10. Garnish: Serve garnished with fresh parsley, if desired.

By following these steps, you’ll create a mouthwatering Mac and Cheese Meatloaf Casserole that will undoubtedly be the star of your dinner table!