In a medium bowl, combine the flour, pumpkin spice, cornstarch, baking soda and salt.
In a separate large bowl, beat together the butter and sugars using an electric hand mixer until creamy and combined. Add in the pumpkin and beat until well mixed.
In a separate small bowl, whisk together the water, oil and baking powder. Add it into the butter mixture and beat until just combined, about 30 seconds.
Add the flour mixture into the butter mixture and stir until well mixed. Stir in the chocolate chips. Your dough will be quite wet and sticky.
Cover and chill for at least 4 hours.
Pre-heat your oven to 350 degrees and line two cookie sheets with parchment or a silpat.
Scoop the dough into 1 Tbsp sized balls (I used a cookie scoop) and place on the pan. Do not flatten them out at all. **
Bake until the top feels set and the edges JUST begin to darken, about 16-17 minutes. Let cool completely on the pan (the set up a lot once cooled!)
DEVOUR!