Grease the inside of a slow cooker with nonstick spray.
In a large bowl, mix together the sour cream, cream of chicken soup, melted butter, cheddar cheese, onion, salt, and pepper.
Add the thawed hash browns and stir until fully combined.
Spoon the mixture into the slow cooker and spread evenly.
Cover and cook on low for 5-6 hours or on high for 3-4 hours.
Just before serving, mix the crushed cornflakes with 2 tablespoons of melted butter.
Sprinkle the cornflake topping over the potatoes and cover for an additional 10-15 minutes.