Preheat the oven to 350° F. Line the bottom of a 9x13 baking pan with parchment, leaving an overhang on all sides to easily lift the bars out of the pan when cool. Spray with non-stick baking spray. Set aside.
In a medium-size bowl whisk the flour, baking soda, cornstarch, and salt together. Set aside.
In a large bowl, mix the melted butter, brown sugar, and granulated sugar together until no lumps remain. Mix in the eggs, and vanilla extract. Pour the dry ingredients into the wet ingredients and mix together until combined. Fold in the chocolate chips, reserving 1/4 cup for the top if desired. (It's just for appearance, you don't have to do this step.)
Transfer dough to the prepared baking pan and spread into an even layer. Sprinkle the top with the reserved chocolate chips.
Bake for 35-40 minutes or until lightly browned on the sides. Test for doneness with a toothpick, if it comes out clean from the center of the pan, the bars are done. Do not overbake.
Let the bars to cool in the pan set on a wire rack for about an hour before slicing.
When cool, lift the bars out of the pan using the overhang on the sides and cut into desired size serving squares.
The number of servings will depend on how large or small you cut the squares.