Preheat your oven to 375°F. Lightly grease a 12 count muffin tin with butter or oil, and set aside.
Peel your potatoes, and wash with cold water to remove any dirt or starch on the surface. You can also leave the skin on and just wash the potatoes. Using a sharp knife or mandoline, cut your potatoes into very thin slices (about 1/16 of an inch).
In a large bowl, combine your potato slices, butter, rosemary, garlic, salt, and pepper. Toss to coat the potatoes in all the seasonings.
Stack your seasoned potato slices in your muffin tin. Bake in the center of your preheated 375°F oven for 45 to 50 minutes, or until knife tender and golden brown on the edges and top. If you find the potatoes stacks are browning too quickly, loosely tent with aluminum foil and continue baking until cooked all the way through.