Can this cake be made in a 13x9 pan instead of two layers?

Yes Regine is correct, I also have baked this in a 9x13 pan and it worked just fine it took longer to bake in the rectangular pan. It takes about 30 minutes in 2 9 inch round pans and I cannot remember how long it took in the rectangular pan. As Regine said I would start testing after about 35 minutes.

I have baked this in a 9x13 pan before with no problems. However, I can't remember how different the time it took to bake was. I think it is 30-35 minutes for 2 9 inch baking pans. Maybe you want to try inserting a toothpick in middle of the cake at the 30 minute mark to check doneness, and adjust accordingly.