Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.

In a large mixing bowl, cream the softened butter (not melted butter) and granulated sugar until light and fluffy.

Beat in the egg and vanilla extract until well combined.

Add the mashed sweet potatoes (they should be cooked beforehand, until fork tender) to the bowl and combine until the mixture is smooth and creamy.

Whisk together the all-purpose flour, baking powder, ground cinnamon, ground nutmeg, and salt in a separate bowl.

Gradually add the dry ingredient mixture to the wet ingredients, mixing until a soft dough forms.

Using a spoon or cookie scoop, roll spoonfuls of dough (knead lightly in your hand) and place them onto a parchment-lined baking sheet, leaving some space between each cookie. Repeat with any remaining dough onto another greased baking sheet.

Gently flatten the cookies onto their prepared baking sheet with a fork or fingers.

Bake in the oven for 15-18 minutes or until the cookies are set and the edges are lightly golden. They should be slightly springy and only light brown.

Remove them from the oven and let the cookies rest on the baking sheet for a few minutes before transferring them to a wire rack to cool completely.

Dust the cooled cookies with powdered sugar before serving.