In a medium saucepan, combine 2 cups milk, ½ cup granulated sugar, ⅓ cup cornstarch, and ¼ teaspoon salt. Heat over medium heat, stirring constantly until thickened, about 10 minutes.

Whisk together 3 large egg yolks in a separate bowl. Gradually add a scoop of the hot pudding mixture to the yolks, whisking vigorously for about 2 minutes.

Pour the tempered egg yolks back into the saucepan. Continue cooking on medium-low heat while stirring for another 3-5 minutes until smooth.

Remove from heat and stir in 2 tablespoons of unsalted butter and 1 tablespoon of vanilla extract until incorporated.

In a serving dish, layer vanilla wafers, sliced bananas, and custard mixture. Repeat until ingredients are used, ending with custard.

Cover with plastic wrap and refrigerate for at least 2 hours before serving.