Melt the butter in a large skillet on medium heat.
Stir in sugar, rum, vanilla, and cinnamon.
Keep stirring until the mixture bubbles.
Add the bananas and optional walnuts.
Cook until the bananas are hot, 1-2 minutes, then serve over a scoop of ice cream.
Very Optional - set the rum on fire after you add the bananas. If the rum doesn't ignite, add 1/2 oz of your favourite flammable alcohol. Do not do this unless you know what you're doing. Only use a long match, or a long lighter. Never put out kitchen fires with water - use a Class B fire extinguisher, or smother with a lid. If you don't have a Class B fire extinguisher handy, don't set your food on fire!