Preheat oven to 350° F. Prepare a 9x13 casserole dish by greasing with butter or nonstick spray.
Saute onion in 1 tablespoon butter until translucent in a medium skillet.
In a large bowl, add frozen hash browns, melted butter, cream of chicken soup, sour cream, grated cheese, cooked onion, salt, and black pepper. Mix together until combined.
Replace medium skillet to the heat and melt the remaining 4 tablespoons butter.
Add in crushed corn flakes and stir to toast about 1 minute. Sprinkle over top casserole.
Bake uncovered for 40-45 minutes or until hot and bubbly. Serve hot.
Video
Notes
Make Ahead + Storage Instructions
To make ahead: Prepare everything, cover, and refrigerate up to 24 hours before baking. Wait to add the cornflake topping until just before baking.To refrigerate: Store leftover funeral potatoes in its original casserole dish, covered with plastic wrap - or in an airtight container for 3-4 days in the refrigerator.To freeze: Assemble the casserole, cover tightly with plastic wrap and aluminum foil, and freeze for up to 3 months. Thaw in the fridge 24 hours before you want to bake it. Bake as normal.