Creating Mac and Cheese Meatloaf Casserole is easy when you follow these definitive steps:

1. Preheat Oven: Preheat your oven to 350°F (175°C).
2. Prepare Meat Mixture: In a large bowl, combine the ground beef, egg, milk, garlic powder, onion powder, Worcestershire sauce, salt, and pepper. Mix well until combined.
3. Add Macaroni: Stir in the cooked macaroni and half of the cheddar cheese.
4. Form Meatloaf: Transfer the mixture into a greased 9×13-inch casserole dish, shaping it into an even layer.
5. Top with Breadcrumbs: Sprinkle breadcrumbs evenly over the meatloaf mixture to create a crispy crust.
6. Bake: Place in the preheated oven and bake for 30 minutes.
7. Add Cheese: Remove from the oven, pour marinara sauce on top (if using), and sprinkle with the remaining cheddar cheese.
8. Finish Baking: Return to the oven and bake for an additional 10-15 minutes or until the cheese is bubbly and golden brown.
9. Cool: Remove from the oven and let it cool for about 10 minutes to set.
10. Garnish and Serve: Optionally garnish with fresh parsley or chives before slicing and serving.

These simple steps will guide you through the process of preparing this incredibly satisfying casserole.