Melt the butter: In a large skillet, melt 1/4 cup of butter over medium heat. Allow it to foam slightly without browning.
Add the sugar and spices: Stir in 2/3 cup of dark brown sugar, 3 1/2 tbsp of rum, 1 1/2 tsp of vanilla extract, and 1/2 tsp of ground cinnamon. Continuously stir until the sugar dissolves and the mixture starts to bubble, creating a syrupy consistency.
Incorporate bananas and nuts: Once bubbling, gently add 3 sliced bananas and 1/4 cup of chopped walnuts to the skillet. Cook for about 1-2 minutes, just until the bananas soften slightly and are heated through.
Flambé the mixture: Carefully ignite the 1/4 cup of banana liqueur in a long-handled lighter or match and pour it over the banana mixture. Allow the flames to subside naturally; this should only take a minute.
Serve: Scoop vanilla ice cream into serving bowls and ladle the warm banana mixture over the ice cream. Serve immediately for the best experience!