Whisk together the sour cream, cream of chicken soup, milk, ½ cup melted butter, salt and pepper.
Combine the thawed hashbrowns, diced onion, 2 cups of shredded cheddar and sour cream mixture.
Spread evenly in a 9x13 casserole dish.
Sprinkle the remaining ½ cup shredded cheddar evenly over the top.
Toss the crushed cornflakes with the ¼ cup melted butter to coat, then sprinkle over the shredded cheddar.
Bake at 350 degrees F for 45 to 60 minutes, until cheese is melted and casserole is bubbly.
Calories are automatically generated. For best results calculate based on your exact ingredients.Crock pot variation: Whisk together the sour cream, cream of soup, milk, butter, salt and pepper. Then combine hash browns, diced onion, 2 cups shredded cheese, and sour cream mixture. Spread evenly into slow cooker. Sprinkle remaining cheese over top and cover. Cook on low for 8 - 10 hours or high for 4 - 6 hours. Top with cornflakes before servings.