Keep a skillet over the heat. Add the butter and wait for it to melt.
Stir brown sugar with cinnamon into the butter. Keep over a medium heat setting and stir cook for a minute or until the sugar has melted into the butter.
Place bananas into the pan without them breaking. Keep over a medium flame and turn the banana carefuly each once so that they are coated with the butter-sugar blend.
Turn stove to high heat and quickly pour in rum, and optionally the banana liquor/liqueur, to deglaze.
Cook banana over high heat on both sides for 2 minutes or so or until the liquor has reduced. Turn the banana only once around because else they can get mushy. *see Notes for flambé
Arrange scoops of vanilla ice cream in a bowl and top with hot banana foster and sauce. Serve up instantly!
*In restaurants they do a flambe with banana foster, which means they ignite the rum in the pan when it's hot over the stovetop. I don't recommend doing it because of safety reasons. Let's leave that to the professionals.