Melt the butter in a skillet over medium heat. Stir in the brown sugar and gently simmer until sugar has dissolved. Remove from heat and stir in whiskey to make a syrup.
Place back on heat, add bananas and coat with syrup mixture. Gently simmer for 5 minutes more to warm the bananas and cook out the alcohol taste.
To serve, pour banana mixture over vanilla ice cream and sprinkle with cinnamon.