Prepare the Meatloaf Base:
In a large mixing bowl, combine ground beef, breadcrumbs, eggs, milk, garlic powder, onion powder, salt, and pepper. Mix until just combined. Avoid overmixing to ensure a tender texture.
Layer the Casserole:
Grease a 9x13-inch casserole dish and press the meat mixture evenly into the bottom to form a base layer.
Add the Mashed Potatoes:
Spread the mashed potatoes evenly over the meat layer. Smooth out with a spatula to create an even layer.
Top with Cheese:
Sprinkle shredded cheddar cheese generously over the mashed potatoes.
Bake:
Preheat the oven to 375°F (190°C). Bake the casserole for 35–40 minutes, or until the cheese is bubbly and golden brown.
Cool and Serve:
Allow the casserole to rest for 5–10 minutes before slicing and serving.