If you don't have a 9"x9" baking pan, you can substitute an 11"x7" pan. An 8" square pan, or a 9" round pan will also work, but they are a bit smaller by volume. So your crust will be thicker, making baking times longer for both layers of the pecan bars. It's all about the math when it comes to changing pan sizes and King Arthur Baking has a great online resource if you need some assistance.