In a saucepan, whisk together cornstarch, 4 tablespoon of sugar, and salt. Then add eggs, milk, and vanilla extract. Cook over medium heat, stirring until thickened.
Remove from heat and let cool. In a separate bowl, whip heavy cream with remaining sugar and condensed milk until stiff peaks form.
Layer Nilla wafers, sliced bananas, and pudding in a dish. Top with whipped cream and refrigerate for at least 2 hours before serving.
Notes
For best results, use ripe bananas. You can also add more layers for extra flavor.