I have a banana cake in which flour does not even make up 50% of the batter.
What Bracha Acharona and Rishona would I make on a piece of the cake?
The bracha achrona is also is al hamichya, for the same reason. Being that there is a significant amount of other ingredients in the cake, although we would make al hamichya even if we eat only a k’zayis of it, it is still preferable to eat enough of the cake that there will be a k’zayis of flour, water etc. without the banana and eggs etc.
O:CH 208-3, M:B ibid 48. Chazon Ish O:CH 26-8, Igros Moshe O:CH 1-71.