Instructions:
- I. Prepare the Custard Base: Gently heat milk, cream, and half the sugar in a saucepan until steaming. Remove from heat.
- In a separate bowl, whisk remaining sugar, cornstarch, and salt. Whisk in egg yolks until pale yellow. Slowly drizzle about 1 cup of the hot milk mixture into the yolks while whisking constantly (tempering).
- Pour the tempered yolk mixture back into the saucepan with the remaining milk. Whisk constantly over medium heat until the mixture thickens significantly and bubbles slowly (about 2–3 minutes after bubbling). Remove from heat.
- Whisk in the cold butter cubes and vanilla until smooth. Cover the surface directly with plastic wrap and allow to cool slightly (about 30 minutes).
- II. Assemble the Pudding: Set oven temperature to 350°F (175°C). Slice the bananas. Arrange a layer of vanilla wafers, top with banana slices, and pour one-third of the cooled custard over. Repeat layering until all ingredients are used, ending with a final layer of custard.
- Bake for 25–30 minutes until the custard is set around the edges. Remove from the oven and let cool slightly.
- III. Make and Finish the Meringue (Swiss Method): Place egg whites, sugar, and cream of tartar in a heatproof bowl set over simmering water (ensure water does not touch the bowl). Whisk constantly until the sugar is fully dissolved and the mixture is very hot to the touch (around 160°F/71°C).
- Transfer the mixture to a stand mixer and whip on high speed until stiff, glossy peaks form and the bowl feels cool to the touch (about 8–10 minutes).
- Dollop the meringue over the warm baked pudding, ensuring it seals all the way to the edges of the dish. Toast the meringue using a kitchen torch until beautifully golden brown, or briefly broil, watching constantly.
- IV. Chill and Serve: Allow the pudding to cool at room temperature for 30 minutes, then chill loosely covered in the refrigerator for at least 1 hour before serving for the best wafer texture.