Rub the inside of a casserole baking dish with garlic. Spray with cooking spray.
Layer half the potatoes in the dish. Pour over two tablespoons of the melted butter. Sprinkle with salt and pepper and then 1/2 cup of the smoked gouda. Repeat for second half of potatoes. Pour milk over potatoes.
Cover tightly with aluminum foil and bake for 1 and 1/2 hours. Uncover and bake for 15 more minutes to brown.
Using a mandoline makes these potatoes extra thin and extra delicious!