Line a cookie sheet with parchment paper.
Mix the flour, salt, cornstarch, baking powder and pumpkin pie spice in a medium bowl. Set aside.
In a separate, large mixing bowl, beat together the melted butter, granulated sugar and coconut sugar, using an electric hand mixer, beat until light and fluffy. Make sure there are no lumps in your coconut sugar!
Add in the pumpkin, egg and vanilla extract and beat again until well combined.
Add the flour mixture into the butter mixture and mix until it forms a wet dough. Cover and refrigerate for 30 minutes. Also, mix together the remaining granulated sugar and pumpkin pie spice in a small plate and preheat your oven to 350 defreees
Once chilled, drop the cookie dough onto the cookie sheet in 1 Tbsp-sized balls. Roll the whole ball in the sugar mixture and place on the cookie sheet, flattening out slightly.
Bake for 13-14 minutes, until the outsides feel just set. The cookies will feel very soft and under baked, but they firm up a lot once cooled!
Let them cool for 10 minutes on the cookie sheet and then transfer to a wire rack to finish cooling.