Mix butter, shortening and sugars until light and fluffy.
Add egg and vanilla and mix until well combined.
Combine flour, cornstarch, baking soda, and salt and mix together.
Mix dry ingredients slowly into wet ingredients and blend well.
If the dough is crumbly, stir in water 1 teaspoon at a time until it just holds together. The dough should not be sticky.
Add in chocolate chips and stir until evenly distributed.
Using ¼ cup measure, scoop out dough and form into a ball. Continue until all dough is balled. Approx 24 cookies.
Place dough in the freezer for 2 hours or up to 3 months.
Place frozen cookie onto parchment lined baking sheet and bake at 350 degrees F for 15 min.
Let cool 2 minutes.