Preheat the oven to 350 degrees F.
In a small to medium bowl, mix together the flour, baking powder, cinnamon and salt. Next, in a medium bowl, cream together the butter and sugar until light and fluffy. Add the eggs and vanilla; and then mix until the mixture is smooth.
To the butter and sugar mixture, mix in half of the flour mixture and the milk. Then, mix in the remaining flour mixture, being sure not to over mix.
In a 12-inch cast iron skillet (*see note below about alternative vessels), melt the butter over medium heat. Mix in the brown sugar and salt and stir until the sugar begins to bubble, about 1 minute. Carefully add the bourbon (the mixture will sizzle!) and mix one more time. Turn off the heat and let stand for a few minutes to cool slightly. Next, arrange the bananas to your liking.
Pour the batter over the bananas, and spread the batter gently so it's nice and even. Transfer the cast iron skillet to the oven and bake for 35-45 minutes or until a skewer comes out clean.
Remove the cake from the oven and allow to cool for 5-10 minutes. To invert the cake, place a (large enough) plate on top of the cast iron skillet and turn both of them over; lift up the cast iron skillet and voila! Your cake!
I like to serve this cake slightly warm with a dollop of whipped cream. And a cup of coffee. Always.