In a medium-sized skillet over medium-low heat, melt the butter. Add brown sugar and whisk until it dissolves. This will take about 3 minutes. Add the vanilla extract, cinnamon, and rum. Cook for an additional 5-7 minutes until the mixture starts to thicken.
While the sauce cooks, slice the bananas.
When the butter/sugar mixture begins to bubble, reduce the heat to low and add the bananas to the pan. Cook for 2-3 minutes.
Remove pan from heat, stir in walnuts, then let the mixture cool a bit to thicken.
Portion ½ cup of vanilla ice cream into 4 dessert bowls.
Divide the bananas foster equally between the four bowls and serve immediately.