I made genoise sponge for Christmas. It looked perfect in the oven but when it was cooling, the middle deflated. I was able to cut it for a layer cake, but there was a definite dip in the middle.
What did I do wrong?
Here's an idea that I use to prevent this from happening, though it's not completely foolproof: As soon as you take the pan out of the oven, hold it flat about 10in above a hard surface such as counter or stovetop and drop the whole thing once or twice. I know this seems sketchy and possibly counterproductive, but it's rooted in science as it breaks apart the cake structure and allows the cake breathe which helps it to not shrink/contract when the air pockets cool. Source: Peter Barham's Science of Cooking. And Harold McGee (in his book On Food and Cooking) recommends baking in tube or bundt pans, then inverting the cake (still in pan) over a bottle like a stand through the central hole when initially cooling so that gravity holds the shape.
Holy moly that is counterintuitive. But worth a try!