If I use frozen and then defrosted bananas for banana cake do I use less water being that the bananas expel a lot of water as they defrost or do I use the same amount of water being that the bananas would expel the water anyways as they cook? (I would have the same question regarding using any frozen and defrosting fruit in cake I suppose)
If you defrost your bananas in a bowl and use all the liquid expelled, then you would follow the recipe as if they were fresh bananas. When the banana cells freeze, the cell walls rupture thus the reason defrosted bananas are mushy and watery. When freezing bananas, freeze them in their peel. It will protect the fruit better than if you peel it first.
(While the banana liquid is clear, it is not just water, it is the juice from the bananas, so you want to use)