I'm baking a 11 x 15 chocolate cake tonight and was wondering what the best amount of batter is to use for this size sheet cake.

I'm using a "cake extender" I saw on here which is adding:

1 c. flour
1 c. white sugar
1 tsp salt
2 c. sour cream
1 egg
1 tsp vanilla

I guess you add this to a prepared mix. So I'll be making 2 mixes + 2 "extenders"----some ppl estimate each combo of mix + extender = 8 cups so would you think 16 cups would be enough for this size pan??

Also, I'm planning on baking this at 325 but not sure on how long. Any suggestions?? I've heard to increase baking time when using any sour cream in recipes.

Thanks so much for any suggestions!! I'm great at the actual decorating process but I'm not so handy in the actual "baking" process unless it's followed as the directions say.

I think you need to consider that all ovens cook differently. I usually fill my pans about 2/3 full. I set the timer for 35-40 minutes and then check. I usually have to bake longer...I just keep checking until it is ready to come out.
traci

Well I use 2 cake mixes for my 11 x 15. That is so that I can cut it and fill it aswell..

I usually mix up 3 but end up having extra batter left over. I either use it for another cake or I make some extra cupcakes. I made about a dozen cupcakes with extra batter this weekend....I ended up having a lady come over to sample on Monday...so that worked out good!!!
traci

I use 3 mixes too. I have plenty left over for another cake.