These questions may seem like a no-brainer to some of you, but I'm not
a baker by any stretch of the imagination so I need help!

I have a recipe for a cake that recommends using two 10x3" round pans
and yields 9 cups of batter. How much of this cake batter would I
need to fill a 11x15x2" rectangular pan? I guess I would fill it up
1/2 way and then bake until it's set in the center and hope for the
best? Would the edges be overbaked by the time the center was set?
Can I prevent this from happening? Is there any way possible that I
can still follow the recipe as is and make 2 sheet cake layers out of
it so I can use a filling (whipped cream type of filling) and still
have it coming out tasty (not dry, crumbly, etc)?

Also, the key in the back of the cookbook says that a 10" round
layered cake will yield 25 servings - does this sound about right? My
daughter is having a birthday party and so I'll need at least 25
servings for kids + adults.

Thanks!

N.