My problem is this:
I'm making a chessboard cake for my husband's birthday. I've baked the 11" square cake; it's rhubarb and polenta (his favourite) but instead of doming as my cakes usually do, it's sagging in the middle.
Now I'm going to need the top of the cake to be completely flat and level to make the chessboard and I don't know what to do to rectify the problem. I was thinking of just sticking loads of ganache on it when I cover it (I always use ganache under fondant) but he's not that keen on lots of ganache. My other option is to make another cake to fill the dip and sandwich them together. But I don't have any more rhubarb! So, I could make a different type of cake but I think that might be weird; when we cut it each slice will be two types of cake!
Can you level it so it has a flat top or would that take off to much height?
Some of the reasons that can cause a cake to sink in the middle are:
2) over mixing
3) baking soda (too much perhaps)
4) cake was disturbed before it had time to set (perhaps by opening oven to soon)
I'm sure there are more but this is what I can think of at this time of the night...
If you level the cake you may be able to see if the cake is underbaked and then make it again if need be. I've never made a rhubarb cake and don't know what polenta is so can't be certain if these contributed in anyway to the cake falling.
I hope your able to salvage your cake but if I were in doubt I'd bake it again.