Preheat the oven to 350°F.
Lightly coat a standard 12-cup muffin tin with nonstick cooking spray.
Place the thinly sliced potatoes in a large mixing bowl.
Add the melted butter, Parmesan cheese, chopped rosemary, garlic powder, salt, and black pepper.
Gently toss the potato slices until they are evenly coated with the butter and seasoning mixture.
Arrange the potato slices in stacks inside each prepared muffin cup. Fill each cup until the potato slices slightly rise above the top of the muffin tin.
Bake for approximately 1 hour, or until the potatoes are tender in the center and lightly golden around the edges.
If the tops begin to brown before the centers are tender, loosely cover the muffin tin with foil and continue baking until fully cooked.
Remove the muffin tin from the oven and allow the potato stacks to rest for a few minutes.
Carefully loosen each stack with a small spoon or knife and transfer to a serving plate.
Sprinkle with additional Parmesan cheese and fresh chopped parsley, if desired, just before serving.
Serve warm.