........making a 12 inch square 2 inch pan how many batches of the recipe would I need.......
You will use 2 batches of my *original* WASC recipe for that size pan.
As for filling - well it depends on what flavor cake you are making
Any fruit filling would be great. I had a wonderful customer who *loved!* bavarian creme filling (I used the sleeved fillings ), in her white cakes - which I thought was very bland
What about cookies & cream OR crush a candy bar (or 2) into b'cream w/some extra flavoring? "simply fruit" jams or jelly or even canned pie fillings are good too.