Brown your Butter: In a saucepan melt the butter over medium heat and continue to cook and swirl until it turns brown, brown bits stick to the bottom of the pan and smells delightfully nutty. Transfer to a bowl to cool (make sure you get all those yummy brown bits too!)
In a large bowl combine flour, baking soda, baking powder, cornstarch, salt, and all spices. Whisk together and set aside.
Combine butter and sugars in the bowl of a stand mixer and beat until thick. Add the egg, and beat to incorporate. Add the pumpkin and mix on medium just until incorporated. Be sure to scrape down the sides of the bowl as necessary.
Reduce the mixer speed to low and gradually add the flour mixture. I usually do 4-5 additions, scraping down the bowl as necessary. Make sure you add the next addition as soon as most of the flour has been incorporated from the last one.
Add the chocolate chips either with the mixer or with a wooden spoon.
Refrigerate overnight. I know, I know. Patience grasshopper. The melted butter makes this step critical. [I did bake some without refrigeration the first night, because I don’t practice what I preach, and they were good but they definitely baked thicker after refrigerating overnight.]
Preheat oven to 350° and line several baking sheets with parchment. I like to use a thin cookie sheet for these cookies because I think they bake up more evenly.
Roll dough into balls approximately the size of a golf ball. Place on a cookie sheet 2 inches apart and bake for 12-14 minutes or until they puff up and the middles are no longer a dark brown (they will be a lighter pumpkin color).
Let cool 5 minutes on the baking sheet and then remove to a wire rack to cool completely. If you are impatient and you eat a cookie too soon, it will seem way underdone. This is how I like them.