Preheat the oven to 350°F (180°C).
Line a large baking sheet with parchment paper, and brush the paper with some of the butter.
Using a mandoline or an electric slicer, slice the potatoes lengthwise very thin. Keep the slices in order, as if you were going to reconstruct the potatoes.
Starting from the side of a potato, place 2 adjacent slices together with sage leaf sandwiched in between.
As the pairs of potato slices are assembled place them close to each other but not overlapping on the baking sheet.
Brush them lightly with butter. Place in the oven and bake 15 to 20 minutes, turning them once as the edges brown.
Remove from the oven and allow them to cool on racks.
Serve or store in an airtight container.
