Preheat your oven to 350°F. Lightly grease a 9x13-inch baking dish and set aside.

Prepare the casserole. In a large mixing bowl, combine the thawed hash browns, sour cream, cream of chicken soup, melted butter, onion powder, kosher salt, shredded sharp cheddar cheese and shredded gruyere cheese. Stir until well combined.

Pour the hash brown mixture into the prepared baking dish, spreading it evenly.

Prepare the topping. In a separate bowl, mix the crushed butter crackers with the melted butter and the shredded sharp cheddar cheese until the crackers are well coated.

Sprinkle the cracker topping evenly over the hash brown mixture.

Bake in the preheated oven for 45 minutes, or until the top is golden brown and the center is heated through. If the topping starts to brown too quickly, lightly tent the dish with aluminum foil to prevent over-browning.

Let the casserole cool for a few minutes before serving.