not sure if this is of assistance but i was looking at custard recipes of recent and his banana custard is mentioned here. dont know about the flan but i guess it would have the same filling.
Primal Kitchen: A Family Grokumentary: Custards!
I like the Son of Grok banana "Caveman Custard" recipe. In my head, I call it "1-2-3 custard" because it requires one can of coconut milk, two bananas, and three eggs (along with a dash of cinnamon).