Follow these straightforward steps to create your Irresistible Mac and Cheese Meatloaf Casserole:

1. Preheat the Oven: Preheat your oven to 350°F (175°C).
2. Prepare the Meatloaf Mixture: In a large mixing bowl, combine the ground beef, breadcrumbs, Parmesan cheese, chopped parsley, egg, garlic powder, onion powder, salt, and black pepper. Mix until well combined.
3. Shape the Meatloaf: Transfer the meat mixture into a greased baking dish and shape it into a loaf.
4. Bake the Meatloaf: Place the meatloaf in the oven and bake for 30-35 minutes until it’s cooked through.
5. Cook the Macaroni: In a separate pot, cook the macaroni according to package instructions. Drain and set aside.
6. Prepare the Cheese Sauce: In a saucepan, melt the butter over medium heat. Whisk in the flour and stir until it forms a paste.
7. Add Milk: Gradually add in the milk while whisking continuously to prevent lumps. Cook until the sauce thickens.
8. Add Cheese and Spices: Remove from heat and stir in the cheddar cheese, mustard powder, paprika, and cayenne pepper (if using). Mix until the cheese is melted and smooth.
9. Combine Mac and Cheese with Sauce: Mix the cooked macaroni into the cheese sauce, ensuring all noodles are coated.
10. Top the Meatloaf: Once the meatloaf is done baking, remove it from the oven and spread the macaroni and cheese mixture over the top.
11. Final Bake: Return the casserole to the oven and bake for an additional 10-15 minutes, until bubbly and golden on top.
12. Serve: Once done, allow the casserole to rest for a few minutes before slicing and serving.

This step-by-step process makes it easy for anyone to create this dish. Get ready to enjoy the warm, cheesy goodness that is embodied in every bite!