Preheat the oven to 350 degrees.
Cream the butter and sugars together in a stand mixer.
Add the egg and vanilla and cream them together.
In a separate bowl, measure 2 cups of flour (240g) and add cornstarch, baking soda, and salt.
Add the dry ingredients to the wet and mix to combine.
Add 2 cups of mixins, depending on what kind of cookie you're making!
Using a medium sized cookie scoop or a 1/8 measuring cup, place balls of dough on a baking sheet.
Cook for 10-11 minutes or until edges just slightly begin to turn golden brown, then remove from oven and place pan on a cooling rack for at least 5 minutes. Allow to cool completely.