For the icing, combine the butter, dark brown sugar and heavy cream in a heavy saucepan and bring the mixture to a rolling boil, stirring constantly.
*With very ripe bananas, you can "mash" them right in the peel - just gently push each banana between your fingers until the whole thing feels smushed. You can then add each one right to the bowl. The mixing of the other ingredients will mash them more. **This makes a fairly large cake. Use a bundt pan that has a 12 cup capacity, otherwise you'll have a mess in your oven. If your Bundt pan is smaller than 12 cups, just pour about a cup of the batter into a small, greased bread pan and bake it along side the Bundt cake. Cake recipe adapted from Food.com Icing recipe adapted from The Hungry Housewife