Soft Chocolate Chip Cookie Bars

Preheat the oven to 350°F. Spray a quarter sheet pan or a 9" x 13" inch metal pan with cooking spray.
In a large microwave-safe bowl, melt the butter. Add the sugars and vanilla and stir well. Add in the egg and egg yolk and whisk to combine.
Sprinkle the flour over the wet ingredients. Sprinkle the baking soda, cornstarch, and salt evenly over the top of the flour.
Stir until the dry ingredients are well incorporated. Add the chocolate chips and stir again until they are well distributed.
Spread the dough into the prepared pan by pressing it evenly all the way to the edges of the pan. Sprinkle over some additional chocolate chips, if desired.
Bake for 28-32 minutes until the edges are golden and the center isn't shiny.
Remove the pan from the oven and allow it to cool for one hour on a rack. Run a knife along the edge of the cookie bars to help loosen them from the pan.
Invert the pan onto a cutting board, then use a second cutting board or serving platter to invert the bars again so that they are face up. Slice into 24 squares with a sharp chef's knife.