Melt unsalted butter in a large skillet over a medium heat. Add dark brown sugar and stir until sugar is melted. Add 1 shot dark rum into the mixture and stir. Add bananas and saute for 4 to 6 minutes. Pour banana liqueur and rest of rum over the mixture. Stir and flambe until flames die out. Sprinkle with cinnamon. Serve over vanilla ice cream immediately.