How to Make It
In a medium bowl, whisk the flour with the cinnamon and salt. In a small bowl, whisk the milk with the eggs, dark rum and 3 tablespoons of the melted butter until smooth. Whisk the wet ingredients into the dry ingredients just until combined; there will be a few lumps. Refrigerate, covered, for 1 hour or overnight.
Preheat the oven to 425°; butter 2 foil-lined baking sheets. Heat an 8-inch nonstick skillet. Pour 1/2 cup of the batter into the skillet, swirl to distribute evenly and cook over moderate heat until set, about 2 minutes. Invert the crêpe onto a prepared baking sheet. Repeat with the remaining batter to make a total of 4 crêpes.
Heat the remaining 2 tablespoons of melted butter in the skillet. Add the bananas and cook over moderately high heat, stirring once, until lightly caramelized but not falling apart, about 2 minutes. Spoon the bananas over the crêpes and sprinkle with the brown sugar. Bake for about 16 minutes, until the sugar is melted and bubbling.
In a bowl, beat the heavy cream with the confectioners’ sugar until firm. Using 2 large spatulas, transfer the crêpes to serving plates. Top with a dollop of the whipped cream and serve at once.