Preheat oven to 375°F (190°C). Spray a 9x13-inch baking dish with cooking spray.
In a large skillet, cook ground beef and onion over medium heat until browned. Drain excess fat.
Stir in cream of mushroom soup, sour cream, and 1 cup cheese. Season with salt and pepper.
Add hash browns and stir until well mixed.
Pour mixture into prepared baking dish and spread evenly.
Top with remaining ½ cup cheese.
Bake for 30–35 minutes, or until hot and bubbly.
Let rest 5 minutes before serving.
