Preheat the oven to 350°F (175°C) and line a baking sheet with parchment paper.

In a large mixing bowl, cream together the softened butter, pumpkin puree, brown sugar, granulated sugar, and vanilla extract until smooth.

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

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

In a small bowl, mix together the granulated sugar and 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 onto the prepared baking sheet, spacing them about 2 inches apart.

Bake in the preheated oven 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.