Preheat oven to 375°F (190°C) and grease a 9x13 inch baking dish.

In a large skillet over medium heat, brown the ground beef and onion until meat is no longer pink; drain excess fat.

In a large mixing bowl, combine the thawed hashbrowns, cream of mushroom soup, cream of chicken soup, sour cream, melted butter, salt, pepper, and garlic powder.

Stir the cooked beef and onion mixture into the potato mixture until well combined.

Fold 1.5 cups of shredded cheddar cheese into the mixture.

Spread the mixture evenly into the prepared baking dish.

Sprinkle the remaining 0.5 cup of cheddar cheese over the top.

Bake for 40 to 45 minutes until the casserole is bubbling and the cheese is golden brown.

Let rest for 5 minutes before serving.