In a medium saucepan, whisk together milk, 1/2 cup granulated sugar, cornstarch, and salt.
Heat over medium heat, stirring constantly until the mixture begins to thicken and bubble.
Temper the egg yolks by whisking in a small amount of the hot milk mixture, then add the yolk mixture back to the saucepan.
Bring the mixture to a gentle simmer, stirring continuously for about 2-3 minutes until thickened.
Remove from heat, stir in butter and 1 teaspoon vanilla extract.
Chill custard base in the refrigerator.
In a separate bowl, prepare instant pudding mix with the remaining 1 cup milk, following package instructions.
Beat cream cheese with powdered sugar and remaining 1 teaspoon vanilla extract until smooth.
Whip heavy cream until stiff peaks form, then gently fold into the cream cheese mixture.
In a large glass dish or bowl, layer vanilla wafers, slices of ripe banana, custard, and then the cream cheese-cream mixture.
Repeat the layering, finishing with a top layer of wafers and banana slices.
Refrigerate for at least 4 hours or overnight to allow flavors to meld and wafers to soften.
Chill until ready to serve; serve cold.