In a medium saucepan, whisk together 1 cup of sugar, 1/3 cup of flour, and a pinch of salt. Set the saucepan over medium heat and smoothly incorporate 4 cups of whole milk while stirring continuously.

Continue to cook the mixture over medium heat for approximately 4-5 minutes, stirring constantly until it thickens and begins to bubble gently. Lower the heat and continue cooking for an additional 2 minutes, then remove from heat.

In a separate bowl, crack 4 large eggs and whisk them until smooth. Slowly temper the eggs with a small scoop of the hot custard mixture, then mix it back into the saucepan and return it to heat for about 2 minutes.

After boiling for 2 minutes, remove the custard from heat and stir in 1 tablespoon of pure vanilla extract. Allow the mixture to cool for about 15 minutes, stirring occasionally.

In an ungreased 8-inch square pan, layer about 25 vanilla wafers, half of the sliced bananas, and pour half of the cooled custard mixture over the layers. Repeat with another layer of wafers, bananas, and the remaining custard.

Cover tightly with plastic wrap and refrigerate for a minimum of 4 hours. For optimal flavor, chill overnight.

Just before serving, crush any remaining vanilla wafers and sprinkle them on top. Serve chilled.