Preheat oven to 425°F.

Spray a 11 x 7-inch baking dish with cooking spray.

Slice the potatoes very thinly, about 1/8-inch thick, using a mandoline or sharp knife.

In a large bowl, combine the sliced potatoes with melted butter, salt, garlic powder, and pepper, tossing to coat.

Arrange half of the potato slices in the prepared baking dish. Sprinkle with 1/2 of the shredded Cheddar.

Repeat with remaining potatoes and cheese.

In a small saucepan, bring milk, thyme, bay leaf, and nutmeg to a boil. Remove from heat and discard bay leaf. Pour the hot milk mixture evenly over the layered potatoes.

Cover with aluminum foil and bake for 45 minutes. Remove foil and bake an additional 15 minutes, or until the top is golden and bubbly.