Instructions:
- Phase 1: Crafting the Custard. In a medium bowl, whisk together the sugar, cornstarch, and salt until combined. Whisk in the 6 egg yolks until the mixture is pale yellow and thick.
- Heat the milk in a medium saucepan over medium heat until steaming, but not boiling.
- Temper the yolks: Slowly drizzle about 1 cup of the hot milk into the yolk mixture while constantly whisking to raise their temperature gradually.
- Pour the tempered yolk mixture back into the saucepan with the remaining milk. Whisk constantly over medium heat until the mixture thickens considerably and coats the back of a spoon (about 5-8 minutes). Do not allow it to boil rapidly.
- Remove from heat. Whisk in the butter pieces until fully melted and smooth. Stir in the vanilla extract.
- Cool the custard: Press plastic wrap directly onto the surface of the custard to prevent a skin from forming. Let it cool slightly for about 20 minutes.
- Phase 2: Assembly & Setting. Prepare the assembly components: slice the bananas into 1/4-inch thick pieces and have the vanilla wafers ready. Preheat oven to 350°F (175°C) if using the meringue topping.
- Begin layering in a 9x13 inch dish: Spread a thin base layer of custard. Follow with a single layer of vanilla wafers, then a layer of sliced bananas. Pour about one-third of the remaining custard over this layer.
- Repeat the layering sequence (wafers, bananas, custard) two more times, finishing the top with the last of the custard.
- Chill: Cover the dish tightly and refrigerate for a minimum of 4 hours, or preferably overnight, to allow the wafers to soften.
- Phase 3: The Meringue Finish (Optional). If using, make the meringue: Beat the 4 egg whites with the cream of tartar until soft peaks form. Gradually add the 1/2 cup of sugar, beating until stiff, glossy peaks form.
- Spread the meringue evenly over the deeply chilled pudding surface. Bake at 350°F (175°C) for 10-15 minutes until the tips are lightly golden brown, or use a kitchen torch for immediate browning.
- Cool the topping slightly and serve. Remember that constant whisking during custard cooking is crucial for a silky texture.