Preheat oven to 350 F.
Combine flour, cornstarch, baking soda and salt and coffee powder (if using) in a bowl, mix well and set aside.
Cream together butter and sugars until smooth.
Add egg and vanilla and blend in.
Add flour mixture, beat for 1-2 minutes.
Stir in chocolate chips.
Drop by tablespoons onto a greased baking sheet and bake for 8-10 minutes, until golden brown around the edges.
As soon as you pull cookies out of the oven, you can add more chocolate chips on top.
Let cool slightly and enjoy.