I made this cake with teff flour. It available at most natural foods stores and
online, but I've given measurements for using all-purpose flour. You might want to reduce the salt to 1/2 teaspoon in the batter if you do. The hardier taste of whole grains seems to call for a little more salt to be added, to my taste.
In place of the vanilla bean, you can use 1 teaspoon of vanilla seeds or paste for the bean. For more on vanilla, check out my
Vanilla FAQs. Your bananas should be ripe but not mushy-soft. They'll sweeten in the caramel. If you want to leave out the rum, you could replace it with fresh lime juice, or simply omit it.
If you don't have a cast iron skillet, this can be made a standard 9-inch (23cm) cake pan (not a springform pan, which would leak during baking). Make the brown sugar topping in a regular skillet or pan, then pour it into a cake pan while it's still warm. Cut and lay the vanilla bean and bananas on top.