Here's the link to the recipe:
Hi thepuffin. It will be fine in a 9 x 13 pan. The cookie will be just a teeny bit thicker. Tricky part is going to be the baking time, so start checking for doneness around 30 minutes or so. They sound amazing!!
The area of an 8x8 is 64, so doubled is 128. The area of a 9x13 is 117 - which is close enough. Like mrslarkin said, it will be slightly thicker, and I'd expect them to take 5 to 10 minutes longer than the directions call for.
Go for it. Agree with above. :)
Same here, I often double a coffee cake recipe that is intended for an 8x8 pan to a 9x13 and it comes out just fine.
Just to say thanks for all the very helpful answers, as I am making this dish for a group!