Melt the butter in a large saucepan. Stir in the brown sugar and 1/2 teaspoon cinnamon. Add the bananas and cook them in the syrup until they just begin to caramelize, but are not falling apart, about 2 minutes. Remove the pan from the heat and carefully add the banana liqueur and the rum. Place the pan back on the heat. Using a long-handled lighter, ignite the pan contents. Stand back as you ignite the pan, the flames may be quite high. Sprinkle cinnamon into the flames, if desired. Shake the pan until flame dies, constantly basting the bananas with the sauce. Place 2 scoops of ice cream in each bowl. Divide bananas and sauce evenly over ice cream.