In a medium skillet, heat 1 tablespoon butter and cook the onion until soft (about 5 minutes)
In a large mixing bowl, combine your hashbrowns, salt, black pepper, chives, sour cream, shredded cheddar cheese, cream of chicken soup, and the cooked onion. Stir well.
Preheat oven to 375.
Put potato mixture into a 9X13 casserole dish and cook in the oven for 30 minutes. Take out and stir the whole casserole well.
Put back into the oven and continue to cook until it's bubbling on the sides and in the middle, about 20-30 more minutes.
Mix your French's onions and cornflakes and 1/4 cup melted butter.
Take the casserole out of the oven and sprinkle the cornflake, onion, and butter mixture on top.
Put back in the oven for an additional 5 minutes, watch carefully so the topping doesn't burn