Preheat oven to 350 degrees and spray a bundt pan with baking spray with flour
Start by caramelizing the bananas .In a skillet melt 4 tablespoons of butter , add sliced ripened bananas and 1/4 cup brown sugar.
Stir the mixture and as it get bubbly and thicken add rum, vanilla and cinnamon. Cook a little longer until it thickens up a bit. Take off the burner and set aside.
In a medium bowl mix flour, baking soda, baking powder , salt and set aside
In a mixing bowl cream together 3/4 cup of softened butter, one cup granulated sugar and egg. Mix until nice and fluffy.
Starting with the flour mixture alternate flour mixture and buttermilk until blended well
Now add the banana and rum mixture and blend well
Pour into the prepared bundt pan
Bake in preheated oven for 50 minutes or until tester comes out clean
Allow to cool in pan for around 10 minutes and flip onto a cake plate and allow to cool completely