In a medium bowl, whisk together the all-purpose flour, cream of tartar, baking soda, salt, ground cinnamon, nutmeg, and ginger.
Using your electric mixer, beat the softened unsalted butter, granulated sugar, and brown sugar until light and fluffy.
Beat in the egg, followed by the pumpkin puree and vanilla extract, mixing until everything is well combined.
Gradually add the dry ingredient mixture to the wet ingredients. Mix on low speed just until incorporated. Avoid overmixing.
Cover the dough with plastic wrap and chill it in the refrigerator for at least 1 hour.
In a small bowl, combine 1/4 cup sugar and 1 tablespoon ground cinnamon for the coating.
Preheat your oven to 350°F (175°C). Scoop tablespoon-sized balls of dough, roll into spheres, then roll each ball in the cinnamon-sugar mixture until coated.
Place coated dough balls on a parchment-lined baking sheet, spacing about 2 inches apart. Bake for 10-12 minutes, until edges are set but centers look soft.
Allow cookies to cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely before enjoying.
