urgent please. important bridal shower cake. its a single tier 12" square. the middle where the core was has a lot of space where the cake shrunk back when it cooled. what can i do about that ? also it broke in two when i was turning it out onto cooling rack. will that totally be ok since covered anyway, or will be an issue when sliced ? should i just rebake into two layers instead of single layer 3" high ?

Got any spare cupcakes? Ice on all sdes and tuck into core space. In future, use the core as a pan, grease. flour, and fill with batter to same level as in the big pan around it. When the cake is done, turn out the cake from core, ice sides, and tuck into hole. Ta da! I have even run out to the store and used pound cake for this when there was no time to do anything else.

HTH