Preheat the oven to 375°F. Grease a 9 x 13-inch baking dish.
Dice the onion. Heat the olive oil in a large skillet over medium-high heat. Add the onion and cook until it begins to soften. Add the ground beef, season with salt and pepper, and cook until browned and cooked through, breaking the meat apart as it cooks. Drain off any excess grease.
2 teaspoons olive oil, 1 medium onion, 1 pound Ground beef
In a small bowl, stir together the cream of chicken soup and milk until combined.
1 can condensed cream of chicken soup, ½ cup milk
Add the frozen mixed vegetables and soup mixture to the cooked ground beef. Stir until well combined, then spread the mixture evenly in the prepared baking dish.
12 ounces frozen mixed vegetables, Salt and pepper to taste
In a large bowl, combine the shredded hash browns, 1 cup of the cheddar cheese, and the melted butter. Spread the hash brown mixture evenly over the ground beef filling. Don't press the potatoes down too firmly.
20 ounces refrigerated shredded hash brown potatoes, 1 cups shredded sharp cheddar cheese, ¼ cup butter
Bake for 30 minutes. Sprinkle the remaining 1 cup of cheddar cheese over the potatoes and bake for another 15 minutes, or until the cheese is melted and the potatoes are golden around the edges.
1 cups shredded sharp cheddar cheese
Let the casserole sit for about 15 minutes before serving. This will let it firm up, but of course, you can dig right in