In a small saucepan, combine the rum, vanilla extract, brown sugar, molasses and cinnamon. Bring the mixture to a simmer and stir to dissolve the brown sugar. Shut off the heat and keep warm on the stove.
Heat a cast iron skillet over medium heat. When the skillet feels pretty hot, add the butter and allow it to brown slightly. Toss in the bananas and arrange them, with a wooden spoon, in a single layer in the pan. Sprinkle with a tiny pinch of salt and cook for about 30 seconds to 1 minute. Turn them on their second side and cook for an additional 30 seconds. Pour in the rum mixture and stir to coat. Serve immediately with vanilla ice cream.