The Preparation
Preheat oven to 350°F.
Dice the onion and sauté in butter and olive oil over medium heat until softened. Season with salt and pepper.
In a large bowl, combine thawed hash browns, cream of chicken soup, sour cream, shredded cheddar, and sautéed onion. Mix well.
Transfer mixture into a baking dish (use an 11x13 for a full batch).
Top evenly with crushed cornflakes.
Bake uncovered at 350°F for 1 hour, until top is golden and crispy and casserole is bubbly.
Let cool slightly before serving.
