Peel and slice the potatoes into thin rounds and place in a large bowl.
In another bowl, mix cream of chicken soup, sour cream, and melted butter. Stir in chopped onion, garlic powder, salt, and pepper.
Pour the creamy mixture over the sliced potatoes and toss to coat.
Transfer the potato mixture into a greased 9x13-inch baking dish.
Sprinkle half of the shredded cheddar cheese over the top.
Cover with aluminum foil and bake for 45 minutes.
Remove the foil, add remaining cheddar cheese and breadcrumbs if using, and bake uncovered for an additional 15-20 minutes until bubbly and golden brown.
Let cool for 10 minutes before serving.
Notes
Store leftovers in an airtight container for up to three days. Reheat in the oven or microwave.