Preheat the oven to 350°F.

Spray a 9x13-inch baking dish with nonstick cooking spray. Set aside.

Set a large skillet over medium-high heat and melt the butter. Once melted, add the thawed hash brown potatoes. Cook, stirring occasionally, until the potatoes are slightly crisp and golden brown, 6-7 minutes. Remove from heat.

In a large mixing bowl, whisk together the eggs, milk, salt, and black pepper. Add the hash brown potatoes and shredded cheese. Fold with a rubber spatula to evenly distribute.

Pour the mixture into the prepared baking dish.

Bake the casserole on middle rack of oven until top is golden brown and a toothpick inserted in the center comes out clean, 40-45 minutes.

Check to see that casserole is done. Remove from oven or add time as needed.

Allow casserole to cool for at least 10 minutes before serving. Cut the casserole into squares, or simply spoon onto plates.