Bloom the gelatin in the 2 tablespoons water.
In a bowl, whisk together the egg, yolks, sugar, and cornstarch.
Heat the milk and vanilla seeds in a saucepan until simmering. Whisk a small amount of the hot milk into the egg mixture, repeat until the milk is warm to the touch, then add the warm egg mixture to the saucepan and bring it to a boil, whisking constantly.
Once the mixture has started to boil, continue to whisk as it boils for 3 minutes. Any less and your custard may weep once it has cooled. Add the bloomed gelatin and whisk until it is completely dissolved. Strain the custard into a large bowl, cover with plastic and cool to room temperature.
Once cooled, fold in the whipped cream, then the sliced bananas and pour into the prepared pie crust. Press plastic right to the surface of the pie and refrigerate for about 2 hours, but this can be made a day ahead.
To serve, cover with the whipped cream topping and chocolate shavings. I used a giant rose tip to pipe the ruffles you see in my photos.