Peel the bananas and slice them about 1 inch thick on a long bias. Heat the sugar, butter and cinnamon together in a medium skillet over medium heat until bubbling. Add the bananas and stir gently to coat. Add the rum and carefully ignite the alcohol with a stick lighter. Step back and let the alcohol burn off. Continue to cook, stirring gently, until the sauce has thickened a little bit and the bananas are slightly softened, 1 to 2 minutes. Divide the bananas and sauce between 2 small bowls. Top with ice cream and serve immediately.
Use extreme caution when igniting alcohol. Remove the pan from the heat source before adding the alcohol. Pour the alcohol into the pan and carefully ignite with a match or click lighter. Return the pan to the heat and gently swirl to reduce the flames.