The specific shape of bábovkas is achieved with a traditional form that has a funnel in the center and ribbed outside. In theory, the hot air in the funnel should prevent the centre from getting gooey, but anyone that ever tried baking one with cream cheese or bananas will agree that is not always the case.
I've tried to make a banana bábovka several times and failed more often than succeeded. The right balance of flour, sugar, milk and bananas seemed crucial and it wasn't until my latest attempt that I finally struck gold. Eventually I decided to add melted chocolate into the batter because bananas and chocolate just work together in terms of flavour and it gave the final result a very nice tint and aroma.