Heat the oven to 425°F with a rack in the middle position.
- Wash the potatoes and pat them dry.
- Cut slits into the potato, stopping just before you cut through so that the slices stay connected at the bottom of the potato. Space the slices 1/4-inch apart.
- Melt the butter and brush the potatoes with half of the butter. Sprinkle potatoes with salt, pepper and thyme.
- Bake the potatoes for 30 minutes. At this point, the layers will start separating. Remove the pan from the oven and brush the potatoes with the remaining butter. Make sure some of the fat drips down into the space between the slices.
- Bake for another 30 to 40 minutes, until the potatoes are crispy on the edges and easily pierced in the middles with a paring knife. Serve immediately