Thank you for your question about baking as bars. I have had the same issue with family requests! I think you should be able to bake these in a cake pan or "jelly roll" pan (15x10x1-inch). I am attaching a link for a cake mix bar that is very different than your cookies, but the times might be helpful.
This is just a guess, since we have never tested this recipe as a bar. I suggest you change to 350°F and watch the baking time starting at about 15 minutes, if you are using the 15x10-inch pan. I don't know how thin the layer of batter will be in the pan, so you might have a fairly short bake time.
I hope you have good results. How nice that the family requests one of your recipes!
Answered 03/29/2013 by Marcia-BettyCrocker