Prepare the Custard: In a medium saucepan, whisk together the milk, sugar, flour, and salt. Cook over medium heat, stirring constantly, until the mixture thickens and comes to a gentle boil. Continue to cook for 1-2 minutes. Remove from heat.

Add Eggs and Vanilla: Gradually whisk a small amount of the hot mixture into the beaten eggs to temper them. Then, slowly pour the egg mixture back into the saucepan, whisking constantly. Return to medium heat and cook for another 2 minutes, stirring constantly until thickened. Remove from heat and stir in the vanilla extract.

Layer the Pudding: In each mini mason jar, start with a layer of vanilla wafer cookies, followed by a layer of sliced bananas, and then a layer of the vanilla custard. Repeat the layers until the jars are filled, ending with a layer of custard.

Chill: Cover the jars and refrigerate for at least 2 hours to allow the flavors to meld and the pudding to set.

Serve: Before serving, you can add a splash of rum or bourbon directly into the jars if desired. Alternatively, provide pocket shots of rum or bourbon so guests can add their preferred amount. Top each jar with a dollop of whipped cream.