Preheat the oven to 350°F (175°C).
Peel and slice the potatoes thinly.
In a large bowl, mix the sour cream, heavy cream, garlic powder, salt, and pepper.
Layer half of the sliced potatoes in a greased baking dish.
Spread half of the cream mixture over the potatoes.
Sprinkle half of the shredded cheddar cheese on top.
Repeat the layers with the remaining potatoes, cream mixture, and cheese.
Mix the crushed cornflakes with melted butter and sprinkle on top.
Cover with foil and bake for 45 minutes.
Remove the foil and bake for an additional 15-20 minutes.
Let the casserole sit for 10 minutes before serving.