In a medium bowl, whisk together sugar, cornstarch, and a pinch of salt. Slowly stir in 1/2 cup of cold milk until smooth, then whisk in the egg yolks until fully combined.

Heat the remaining milk in a saucepan over medium, bringing it just to a simmer. Gradually whisk the yolk mixture into the hot milk, stirring constantly until thick enough to coat the back of a spoon (about 3–4 minutes). Remove from heat and stir in vanilla extract.

Transfer the custard to a bowl and press plastic wrap directly onto its surface to prevent a skin from forming. Let it cool to room temperature, then refrigerate until fully chilled, about 20–30 minutes.

In a chilled mixing bowl, beat the cold heavy cream with powdered sugar until soft peaks form—this creates a light, fluffy topping for our pudding.

In a large trifle dish or individual cups, layer half the vanilla wafers, banana slices, and chilled custard. Repeat the layers and finish with the whipped cream on top.

Chill the assembled pudding for at least 1 hour to let the flavors meld and wafers soften slightly. Just before serving, add extra wafers or a drizzle of caramel sauce if desired.