In a saucepan, combine cornstarch, 4 tablespoon sugar, and salt. Whisk in eggs and milk until smooth. Cook over medium heat, stirring constantly, until thickened. Remove from heat and stir in vanilla.
In a mixing bowl, whip cold heavy cream and remaining sugar until soft peaks form. Fold in sweetened condensed milk.
Layer Nilla wafers, sliced bananas, custard, and whipped cream in a serving dish. Repeat layers and finish with whipped cream on top.
Chill for at least 2 hours before serving.
Notes
For best results, use ripe bananas and chill the pudding overnight.