For the pudding: Boil the milk and rum, add the bloomed gelatin, pour over the white chocolate and emulsify with a hand blender. Slowly stream in the cream and banana. Lay plastic wrap on top and let set in the fridge for 4 to 6 hours.
Temper your chocolate: Place two-thirds of the chocolate in a microwave-safe bowl. Microwave on medium in 30 second intervals until fully melted, about 3 minutes. The temperature of the chocolate should be around 120 degrees F. Add remaining one-third of the chocolate and stir until fully incorporated. Keep stirring until the chocolate reaches 85 degrees F. You can test it by holding the chocolate covered spatula to your lower lip. When it no longer feels warm, the chocolate is ready. You can warm it SLIGHTLY, to 90 degrees F, to make it more fluid. This can be done by microwaving it in 2 second intervals. I am not joking - 2 seconds, no more! Keep the chocolate on a heating pad set to low if you are not going to use it for a while. Make sure the temperature stays between 85 and 90 degrees F. If it goes over, you will have to start the process again. And you DON'T want to do that.
Dip the water balloons in the tempered dark chocolate. Swirl off the excess and let crystallize on a parchment paper-lined baking sheet.
For the creme fraiche: Whip the heavy cream with the creme fraiche, powdered sugar and vanilla seeds to soft peaks.
To assemble: Once hard, pop the balloons. Pipe in the pudding and top with whipped creme fraiche. Serve immediately or store in the fridge.