In a large mixing bowl, add 3 cups of spooned and leveled flour. Then remove 2 Tablespoons of the flour (either discard or add it back to the bag) and add 2 Tablespoons of cornstarch. Add the rest of the dry ingredients: baking soda, baking powder, salt, and pumpkin pie spice. Whisk or sift the dry ingredients, so there are no lumps.
In a stand mixer (with paddle attachment) or using an electric handheld mixer, cream together the butter and sugar until light and creamy. It should take about 1 – 2 minutes.
Add the egg, yogurt, pumpkin puree, and vanilla extract. Beat until combined. Add the flour in 3 different increments on low-speed or medium-low. Stop beating as soon as the last bit of dry flour is no longer visible. Scrape the sides of the bowl with a spatula and make sure all flour is combined.
Cover to bowl and chill for at least 20 minutes and up to 1 hour.
Preheat the oven to 350°F. Line two cookie sheets with parchment paper. Set to the side.
Using a cooking scooper, portion out about 2 Tablespoons of dough for each cookie. Roll and flatten them to about ½ inch thick.
Bake for 8 - 9 minutes. They will look underdone, puff up, and be almost barely golden on the bottom. Remove from the oven and let them sit for 5 mins on the baking sheet before transferring them to a wire rack. I like my cookies a little underdone and soft, so I baked for 8 minutes, but some gf flours can have the slightest graininess, so you can bake up to 9 - 10 minutes if needed.
While the cookies cool, make the frosting by placing all ingredients in a large mixing bowl and beating with a handheld electric mixer on medium for 1 – 2 minutes until fluffy and smooth. You can also you a stand mixer with the paddle attachment.
Make sure your cookies are completely cool before frosting! Dust with extra pumpkin spice, and enjoy!