The amount of fat in the cookie dough or batter affects how easily the baked bar cookies can be removed from the baking pan. Follow recipe directions, and lightly spray the pan with no-stick cooking spray. After you are finished baking, make sure the baking pan is washed well – any cooking spray left on the pan will become sticky and can cause cookie bars to stick the next time you bake with it. While cooling bar cookies completely will make it easier to remove them from the pan, be sure to remove the bars as soon as sufficiently cooled. Store them in an airtight container to avoid having the bars dry out.