Preheat your oven to 375F, then whisk together the flour, cornstarch, baking powder and salt in a bowl.
In a separate bowl, use a mixer to cream the butter, sugars, and vanilla extract until light and fluffy.
Gradually fold in the dry ingredients to the wet ingredients until a thick batter forms. Pour in the espresso and mix well.
Sprinkle in the instant coffee powder and chocolate chips and fold to combine.
Smooth out the batter in a parchment lined 8x8 baking sheet.
Bake for 25 minutes or until you can insert a toothpick and it comes out clean.
This will make about 16-20 bars.