Prepare the hash browns. Thaw the frozen shredded hash browns completely, then squeeze out as much excess water as possible. Preheat the oven to 350°F.
Brown the ground beef. Cook the ground beef in a large skillet over medium-high heat until browned and fully cooked. Remove the beef, draining excess grease but leaving a little in the skillet.
Cook the onions. Add the diced onion to the skillet and cook until softened and translucent.
Prepare the creamy mixture. In a large mixing bowl, combine the cream of chicken soup, sour cream, salt, and black pepper.
Combine the ingredients. Add the thawed hash browns, cooked ground beef, and onions to the creamy mixture. Stir until everything is evenly coated.
Assemble the casserole. Spread the mixture evenly into a 9×13-inch baking dish. Sprinkle the grated sharp cheddar cheese over the top.
Bake. Bake uncovered at 350°F for approximately 45 minutes. Allow the casserole to rest briefly before serving.