• Sift together flour, cream of tartar, baking soda, salt and pumpkin pie spice; set aside.
• Cream the butter and 1 1/2 cups sugar at medium speed until light and fluffy, about 2 minutes. Scrape down the sides of the bowl with a rubber spatula if needed.
• Add the egg and beat at medium speed until combined. Add the pumpkin puree and beat at medium speed until thoroughly incorporated.
• Add the dry ingredients and beat at low speed until just combined, scraping down the bowl as needed.
• Cover the dough and refrigerate for at least 20 minutes. This allows the butter to firm up a little bit so it will be easier to roll the cookie dough into the sugar spice coating before baking.

While the dough is chilling preheat the oven and prepare the baking sheets:

• Adjust the oven racks to the upper-and lower-middle positions and preheat the oven to 400 degrees F.
• Line two baking sheets with parchment paper; set aside.
• Place the remaining 1/4 cup sugar and cinnamon for rolling in a shallow bowl. Roll a heaping tablespoon of dough into a 1½-inch ball, roll the ball in the sugar mixture, and place it on the prepared baking sheet.
• Repeat with the remaining dough, spacing the balls about 2 inches apart
• Bake the cookies, one sheet at a time, until the edges are set and just beginning to brown but the centers are still soft and puffy, 10 to 12 minutes, rotate the baking sheet halfway through the baking time.
• Cool the cookies on the baking sheets about 5 minutes; using a metal spatula, transfer the cookies to a wire rack and cool to room temperature.
• Store in an airtight container, or freeze for longer storage.