In saucepan, combine purple yam with salt and 1000 g water, bring to simmer over low heat for about 25 minutes or until potatoes are fully softened.

In separate mixing bowl, whisk water, potato starch, and purple yam extract to form slurry, then whisk into simmering purple potato mixture to thicken.

Continue cooking for about 30 seconds to fully hydrate starch, then transfer to blender.

Blend on high speed until smooth, then spread in thin, even layer on Silpat to dehydrate.

Fry at 180°C to crisp, season with salt, then reserve in dehydrator for service.