Preheat the oven to 350°F. Butter a 9×13-inch baking dish. Make sure your potatoes are mostly thawed and drain any excess water.

In a medium bowl, stir together the hash brown potatoes, sour cream, cream of chicken soup, green onions (or onion powder), salt, pepper, melted butter, and shredded cheese until combined. Spread into the baking dish. Top with extra cheese, if desired.

Spread the crushed cornflakes over the top. Drizzle with melted butter. Bake for 30 to 40 minutes, or until golden brown and bubbling hot. If using cubed potatoes instead of shredded hash browns, bake for 40 minutes.

Let rest for 5 minutes before serving. Enjoy while warm!