Position oven rack in center of oven and preheat to 350°F. Grease a shallow 2 to 2½-quart baking dish with softened butter.
If you have a mandoline slicer, it is recommended for cutting the potatoes, as it will produce very thin slices of the same thickness, which promotes even cooking.
Potato slices will start to brown if exposed to the air too long, so if you're not assembling the dish immediately, you may put the potato slices in a bowl of cool water to prevent browning. Drain and pat dry before proceeding with recipe.