Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper or a silicone baking mat.

In a medium bowl, combine the mashed sweet potato and egg. Whisk or stir until smooth and well blended.

Add the oat flour to the bowl and stir until a soft dough forms. The dough should feel like soft Play-Doh and not be sticky. If it is too sticky, add a tablespoon of oat flour at a time until it comes together.

Lightly flour your work surface with a little oat flour. Turn the dough out onto the surface and gently knead it a few times until smooth.

Roll the dough to about 1/4 inch thickness using a rolling pin.

Use a small round cookie cutter or the rim of a shot glass to cut out coin-shaped cookies. Gather and re-roll scraps as needed until all the dough is used.

Arrange the dough coins on the prepared baking sheet, leaving a small amount of space between each cookie.

Bake for 20 to 25 minutes, or until the cookies are set and lightly golden on the bottom.

Carefully flip each cookie over and return the baking sheet to the oven. Bake for an additional 10 minutes to help dry and crisp the cookies.

Remove the baking sheet from the oven and let the cookies cool completely on the pan. They will continue to crisp as they cool.

Once fully cooled, store the cookies in an airtight container at room temperature for up to 5 days, or refrigerate for longer storage.