In a medium bowl, stir together the oats, flour, cinnamon, baking soda, nutmeg, and salt; set aside.
In a separate large bowl, cream the butter and brown sugar together until smooth. Add the egg, sweet potato, and vanilla and mix well.
Add the oat mixture to the butter mixture and stir until thoroughly combined. Fold in the chocolate chips.
Cover and chill for at least 1 hour (or up to overnight).
Preheat the oven to 350°F (180°C), or 160°C for a fan oven. Line 3 baking sheets with parchment paper and set aside.
Drop the cookies by a small cookie scoop (about 1.5-2 tablespoons of dough) 2” apart on the prepared baking sheets. Press extra chocolate chips on top if desired.
Bake in the preheated oven for 9-11 minutes, or until the cookies are lightly golden and have puffed up.
Allow it to cool for 5 minutes before transferring the cookies to a wire rack to cool completely.
Notes
These cookies are thick, and not meant to spread very much. Your cookie dough should be thick when it's finished.
Chilling the dough: Give the sweet potato cookie dough at least an hour to chill in the fridge. If needed, you can keep the dough in the fridge for up to a day before baking the cookies.
My favorite way to make sweet potato puree or mashed sweet potatoes is to peel and cube the potatoes, then steam them until they're soft. Mash by hand or use a food processor to get them nice and smooth.
Use a cookie scoop: This will help to ensure that all of your cookies are the same size and shape. For this recipe, I'm using a small scoop that holds about 1.5 tablespoons of dough.