Preheat your oven to 425°F (220°C).
In a large bowl, combine the melted butter, salt, black pepper, and thyme leaves if using.
Layer half of the potato slices in a greased 9-inch round baking dish, slightly overlapping them.
Brush half of the butter mixture over the first layer of potatoes.
Add the remaining potato slices on top, again overlapping them.
Pour the remaining butter mixture over the top layer of potatoes, ensuring they are well coated.
If desired, sprinkle the grated Parmesan cheese over the top for added flavor.
Cover the dish with aluminum foil and bake in the preheated oven for 30 minutes.
Remove the foil and bake for an additional 20-25 minutes, or until the potatoes are golden brown and tender.
Let it cool for 5 minutes before slicing and serving.