In a medium bowl, whisk together almond flour, tapioca starch, pumpkin pie spice, cream of tartar, baking soda, and salt until uniform.
In a large bowl, beat the coconut sugar, melted coconut oil, pumpkin purée, and vanilla with an electric mixer on medium to medium-high speed until smooth.
Add the egg yolk and beat on medium-high until the mixture is ribbony, thick, and lighter in color (about 2 minutes).
Add the dry mixture to the wet and mix on low just until combined. The dough will be soft but cohesive.
Cover and refrigerate the dough for at least 2 hours (or overnight) until firm enough to scoop and roll.
When ready to bake, heat the oven to 375°F (190°C) with a rack in the middle. Line two rimmed baking sheets with parchment.
In a small bowl, stir together the coating ingredients.
Using a medium disher, divide the dough into 16 equal portions, about 1¼-tablespoon each. Use your hands to roll each portion into a round ball. Next, coat each ball generously in the spiced sugar.
Arrange 8 cookies per baking sheet, spaced about 2 inches apart. Bake one tray at a time in the center of the oven for 9 to 11 minutes, until edges are golden and centers are soft but set. Always use a cool tray—never scoop dough onto a hot sheet pan or the cookies will overspread.
Let cookies rest on the baking sheet for 10 minutes before transferring to a wire rack to cool completely. Enjoy!