If you want to top the cake with a fresh banana slice, toss the slices in lemon juice to prevent them from turning brown.
It is recommended to bake one cake first and time it to adjust baking duration based on your oven.
Taste and adjust powdered sugar amount in whipped cream as you like.
Remove a bit of the cake off the top if it fills too much of the mini pan, it's not the end of the world if you have to do that after baking the cakes to remove a bit of cake to make space for the milk mixture that soaks into the cake.