1: Preheat the oven to 400°F and place a cast-iron pan inside to heat.
2: In a blender, combine the milk, egg, vanilla, sugar, flour, and salt.
3: Remove the cast-iron pan from the oven and melt 3 tablespoons of butter in it. Pour in the batter and bake for 25 minutes until golden and puffed.
4: Meanwhile, in a pan over medium heat, melt the remaining butter. Stir in the cinnamon, remaining vanilla, and a pinch of salt. Once the butter starts to simmer, add the rum, orange juice, and zest. Cook until the liquid reduces by half.
5: Top the Dutch baby with the caramelized bananas and finish with a dusting of powdered sugar.
