Preheat the oven to 375°F. Grease a 9x13-inch baking dish.
In a large skillet, cook the ground beef and diced onion over medium-high heat, stirring occasionally, until the beef is browned and the onion is softened, about 6 to 8 minutes.
1 pound ground beef, 1 medium onion
Add the minced garlic, thyme, smoked paprika, salt and pepper to the skillet. Stir to combine and cook for an additional 1 to 2 minutes, until fragrant.
3 cloves garlic, 1 teaspoon dried thyme, 1 teaspoon smoked paprika, ½ teaspoon fine sea salt, ¼ teaspoon fresh ground black pepper
In a separate bowl, whisk together the cream of mushroom soup, sour cream, and beef broth until smooth.
10 ½ ounces cream of mushroom soup, 1 cup sour cream, 1 cup beef broth
Spread half of the thawed hash brown potatoes in an even layer in the prepared baking dish. Top with the cooked ground beef mixture, followed by one cup of the shredded cheddar cheese.
32 ounces frozen diced hash brown potatoes, 2 cups shredded cheddar cheese
Pour the soup mixture evenly over the cheese, then top with the remaining hash brown potatoes.
In a small bowl, combine the remaining one cup of shredded cheddar cheese, Parmesan cheese and chopped parsley. Sprinkle this mixture evenly over the top of the casserole.
2 cups shredded cheddar cheese, ½ cup grated Parmesan cheese, ¼ cup chopped fresh parsley
In another small bowl, mix the Panko breadcrumbs with the melted butter. Sprinkle the breadcrumb mixture over the cheese topping.
½ cup Panko breadcrumbs, 2 tablespoons unsalted butter
Bake the casserole, uncovered, for 45 to 50 minutes, or until the top is golden brown and the casserole is bubbling around the edges.
Remove the casserole from the oven and let it cool for 5 to 10 minutes before serving.