Place the sugar, cornstarch, and salt in a medium bowl and whisk to combine.
Whisk in the eggs until the mixture is combined.
Place the milk, cream, vanilla pod, and vanilla seeds in a small pot and place over low heat until steamy and just beginning to simmer.
Temper the egg mixture by whisking in a little of the hot liquid in, until it becomes very warm.
Transfer the mixture back to the pot and continue to cook, whisking constantly, until it becomes thick and comes to a slow bubble.
Immediately pour the pudding through a fine mesh strainer and into a heat-safe bowl, using the back of a ladle to push the mixture through the sieve.
Whisk in the vanilla extract and butter, then press plastic wrap directly onto the surface of the pudding (this prevents a skin from forming), and chill for 4 hours.
Line the bottom of a 1.5-quart serving dish with about half the vanilla wafers, then spread half the pudding in an even layer on top.
Peel & slice the bananas and toss them in the lemon juice, then arrange about half the slices over the pudding.
Whip the cream and powdered sugar together until medium peaks form, then spread about half the whipped cream over the sliced bananas.
Repeat, layering vanilla wafers, pudding, bananas, and whipped cream.
Crush a handful of vanilla wafers into crumbs, and sprinkle them on top of the whipped cream, for garnish.
Chill the banana pudding until the cookies have gone soft (about 4 hours).