There is a big difference between a 9x13 and a jelly roll pan. Which size pan was used for this recipe?

My pan was 11 x 17. I spread the better as thinly as I could. It didn’t quite reach the edges but I had a feeling it would spread, and it did. I don’t think I would use a smaller pan as the cookies would be more cake-like and less like a cookie bar.

Actually, both are simply rimmed baking sheets. They come in a variety of sizes, though jelly roll pans are usually smaller versions. My jelly roll pan is 10 1/2 x 15 1/5, which is actually a bit larger than my 9 x 13 rimmed baking sheet in terms of square inch area. You could successfully bake the bars in either version, though those in my jelly roll pan would be a bit thinner than those baked in the rimmed sheet pan. So you can take your choice, really. Baking times would be slightly different, obviously, but baking times listed are really only guidelines anyway- and you know your own oven best to judge on that.