Preheat oven to 250F (130C). Line one or more baking sheets with parchment paper (the "or more" part just depends on the quantity and size of your sweet potatoes, so you may need more than one baking sheet). Clean any excess dirt from the outside of the sweet potatoes. 

Slice the sweet potatoes into either coins or strips (the strips are nice if you want bigger sized treats, we made coins this time - see photo). Be sure that the coin or strip is no thinner than 1/4 inch. If they're too thin, they'll become too crunchy and not chewy enough. 

DO NOT APPLY ANY OILS OR SEASONING. 

Arrange the coins or strips in a single layer on the baking sheet(s) and bake for 2.5 to 3 hours, flipping halfway through. When they are done, they should be shrunken, dried out, and chewy in the middle. Let them cool, then store them in an airtight container for up to three weeks.