In the bowl of a stand mixer or in a large bowl with a hand mixer, cream butter, ¾ cup sugar, and pumpkin puree together on medium speed for about 3 minutes. Beat egg into the mixture.
In a separate medium bowl whisk flour, cream of tartar, baking powder, and salt together.
Blend the dry ingredients into the wet ones in two separate batches, until they’re completely combined, taking care not to over-mix. Cover mixing bowl and put it in the fridge for 1 hour to chill.
Preheat oven to 400 degrees and line two baking sheets with parchment paper or Silpats.
On a plate, mix together 1 ½ Tbsp sugar and 1 Tbsp cinnamon together. Using about 1 Tbsp dough at a time, roll dough into balls. Place balls on cookie sheet with about an inch of space between them.
Bake for about 10 minutes, until cookies are fully baked, but still soft. Let cool in the pan for a couple minutes, before moving to wire racks to cool completely.