In a saucepan, whisk together the sugar, cornstarch, and salt.
Whisk in the milk, ½ cup heavy cream and egg yolks until smooth.
Place over medium heat, and cook, stirring frequently until the pudding bubbles and thickens, about 8-10 minutes. It should coat the back of a spoon.
Once thickened, cook for an additional minute while whisking. Remove from the heat and stir in the butter, one tablespoon at a time. Mix in the vanilla.
Pour the pudding through a fine-mesh sieve over a heat-proof bowl for the silkiest texture.
Press plastic wrap directly onto the surface of the custard to prevent a skin from forming. Allow to cool for 1 hour, then place in the fridge to chill for 2 hours.
In a mixing bowl beat 1 1⁄4 cups heavy cream, powdered sugar and vanilla extract on low speed until the powdered sugar is incorporated. Increase the speed to medium-high and whip until medium-stiff peaks form, about 3-4 minutes. Chill until ready to use.
Remove the pudding from the refrigerator and whisk well until smooth. Set aside. Fill the bottom of a 2-quart dish with a layer of wafers.
Slice 1-2 bananas into ¼-inch thick coins and place over top of the wafers. Top with half of the pudding.
Repeat with the remaining wafers, banana slices, and pudding. Cover with plastic wrap and chill for 3 hours or overnight.
Once chilled, spread the whipped cream over the pudding. Top with additional banana slices and crushed vanilla wafers just before serving.