Prep the basics: Line two baking sheets with parchment. In a medium bowl, whisk the flour, cream of tartar, baking soda, baking powder, salt, cinnamon, nutmeg, and ginger.
Cream the butter and sugars: In a large bowl, beat the softened butter with the granulated and brown sugars until light and fluffy, about 2–3 minutes.
Add yolk, vanilla, and pumpkin: Mix in the egg yolk and vanilla until smooth. Add the pumpkin puree and beat until combined.
The mixture may look slightly curdled—this is normal.
Combine wet and dry: Add the dry ingredients in two additions, mixing on low just until no streaks of flour remain. Do not overmix.
Chill the dough: Cover and chill for 30–45 minutes. This helps the cookies bake thicker and reduces stickiness for easier rolling.
Make the coating: Stir together sugar, cinnamon, and a pinch of nutmeg in a small bowl.
Preheat the oven: Heat to 350°F (175°C) while the dough chills.
Shape and roll: Scoop 1 1/2-tablespoon portions (a medium cookie scoop).
Roll into balls, then coat generously in the cinnamon-sugar mixture.
Space and bake: Place on prepared sheets, leaving about 2 inches between cookies. Bake 10–12 minutes, until edges are set and the tops are puffed but still soft in the center.
Cool: Let cookies rest on the sheet for 5 minutes, then transfer to a rack to cool completely. They’ll settle into that classic crackly top as they cool.