First start by preheating the oven to 350F, then line your baking sheet with parchment paper and set aside.
In a medium bowl add in the flour, cornstarch, baking soda, and salt, and whisk until incorporated then set aside.
In a stand mixer bowl, using a paddle attachment cream together the butter and both the brown sugar and the granulated sugar on medium high speed or until the mixture becomes light and fluffy. You can also do this using a hand mixer!
Add in the egg, water and vanilla and mix just until combined, 30 seconds- 1 minute.
Add in the dry ingredients to the butter mixture and beat on medium low speed just until combined. Do not over mix the cookie dough! At this stage add in the cup and a half of leftover halloween candy and fold.
Using an ice cream scooper, shape the dough into 10 equally sized balls, and place them on the parchment covered baking sheet. Chill in the fridge for 10-15 minutes. ( this will keep the cookies from spreading too much and turning flat when you bake them! )
Bake the cookies for 12-14 minutes of until the edges are set. The center of the cookie might look a bit undercooked but don't worry The heat will continue baking it when you pull it out of the oven.
Let the cookie cool down on the baking sheet for 5-10 minutes before transferring them to a cooling rack to finish cooling. Enjoy!
I personally like these cookies a few hours after they've cooled down because It allows all the flavors to settle in even better!