Cornstarch is a common ingredient in cookie recipes that helps to provide structure and hold the cookies together. It also contributes to the chewiness factor and makes cookies thicker. Cornstarch is not used as a thickening agent in cookies, but it can help to soften the rigid proteins of the flour, resulting in a light and chewy texture. When added to the dry ingredients, cornstarch can prevent cookies from spreading too much while baking, resulting in a more compact, thick cookie that typically yields a chewier outcome. The amount of cornstarch used in a cookie recipe can vary, but it is typically around 1/2 to 2 teaspoons per cup of flour.