all in one cake?

[Cha]

I need to make ds (2 on wed) a birthday cake. I only have one cake tin, about 9". I have been told that the all in one cake is the easiest - I am no master baker, ho ho. Can I make a big 9" cake and cut it in half and put jam in the middle? Or will it not rise properly? Or should I just buy two more cake tins but smaller?
Sponge is fine, and have cocoa powder to make it chocolatey. All suggestions welcome!

I use a larger tin than specified but usually make 2 cakes rather than cut one in half (only have one tin though!)

I made one for DS on Friday in this size tin.
5 eggs and equal amounts of butter/marg, soft dark brown sugar, SR flour and about 175g cocoa and a bit of milk. Creamed sugar and butter, add eggs and then flour and cocoa. Put milk in at end as necessary.
Cooked it in oven on about 160 C. for about an hour or so (maybe longer). The middle was a bit squidgey to be honest but I cut it in half when it was cold and sandwiched it together with buttercream and it was yummy !
Good luck

my cakes are not great risers so i would always do two seperate tins and sandwich them together