Step 1

Preheat oven to 375 degrees. In a medium bowl, whisk together flour, baking soda, cream of tartar, salt, and nutmeg.

Step 2

In a large bowl, whisk together butter, granulated sugar, and pumpkin until smooth. Add egg and vanilla and whisk to combine. Add flour mixture and stir to combine, about 2 minutes.

Step 3

In a small bowl, whisk together sanding sugar, cinnamon, and allspice. Drop heaping tablespoons of dough into sugar mixture and roll into 1 1/2-inch balls. Transfer to parchment-lined rimmed baking sheets, 3 inches apart. Using a spatula, flatten balls to just under 1/2 inch thick. Sprinkle with more sugar mixture.

Step 4

Bake, rotating sheets halfway through, until light golden and firm to touch, 10 to 12 minutes. Let cool 5 minutes on sheets, then transfer to a wire rack and let cool completely. Cookies can be stored in an airtight container up to 3 days.