I am making an open book cake for a bridal shower in June. They expect 40 people to be there. I thought I could bake the cake in my 11x15 jelly roll pan (It's about 1/2 in high), so I wouldn't have to torte the layers to add filling. Will this work? Does anyone know how long I would have to bake the cake? Will it get too done on the outside before the middle is done?

not a good idea, you will end up with spillover and other problems, use a regular size 11x15 but don't fill it as much as you normally would and you won't have to torte if you make 2. HTH