I actually tested this out, and while it technically worked, I found that the baking dynamics just didn't produce as nice a texture or look in these bars in the smaller batch size. If you do want to try to make a half batch in an 8-inch square, be sure to check the bars quite early, starting around 25 minutes in, as they will bake for a significantly shorter amount of time. However, for the best experience, I recommend sticking with the 9-inch x 13-inch pan and just passing out your extra bars to neighbors if you feel like it's too big of a batch for you. Alternatively, you could always search out a recipe designed for a smaller pan originally.