Begin by preheating your oven to 350°F (175°C). In a medium-sized bowl, whisk together the flour, pumpkin pie spice, cinnamon, baking soda, cream of tartar, and salt until well blended. Set this dry mixture aside.

In a separate large bowl, using an electric mixer, cream the softened butter with the coconut sugar and brown sugar until the mixture is light and fluffy. Add the egg yolk and vanilla extract, beating until smooth. Incorporate the pumpkin puree, ensuring to scrape down the bowl as needed to fully combine the ingredients.

Gradually add the dry flour mixture to the wet ingredients, mixing just until everything is well combined. Cover the bowl and refrigerate the cookie dough for about 30 minutes to firm up.

While the dough chills, line a baking sheet with parchment paper or a silicone baking mat. In a small bowl, mix together the coconut sugar and pumpkin pie spice for the sugar coating.

Once the dough is ready, remove it from the fridge and use a cookie scoop to portion out dough balls. Roll each ball in the pumpkin spice sugar mixture, ensuring they are evenly coated. Arrange the cookies on the prepared baking sheet; they don’t spread significantly, so you can place them relatively close together.

Bake in the preheated oven for approximately 12 minutes, or until the edges are set and the tops look slightly cracked. Allow the cookies to cool on the baking sheet before transferring them to a wire rack to cool completely. Repeat the baking process with any remaining dough. Store the cooled cookies in an airtight container in the refrigerator for up to one week.