Preheat the oven to 350°F (175°C).

In a mixing bowl, combine pumpkin puree, brown sugar, granulated sugar, and softened butter. Mix until smooth.

Add the egg and vanilla extract, and mix until well combined.

In another bowl, whisk together flour, baking soda, cream of tartar, salt, cinnamon, and nutmeg.

Gradually add the dry ingredients to the wet ingredients, mixing until just combined.

In a small bowl, mix together the granulated sugar and ground cinnamon for the coating.

Using a cookie scoop, portion out the dough and roll each ball in the cinnamon sugar mixture.

Place the coated dough balls on a baking sheet lined with parchment paper, spacing them about 2 inches apart.

Bake for 10-12 minutes, or until the edges are set but the centers are still soft.

Remove from the oven and let cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely.