Bring flour, sugar, salt, milk, and vanilla extract to a pot and boil under medium heat. Whisk continuously throughout this whole time to prevent mixture from browning and sticking to the bottom of the pot. Once it comes to a boil, lower heat to medium low and cook until it reaches a slightly thicker consistency. Don't forget to whisk continuously! Remove from heat when it is done.
Slowly add pudding mixture a few tablespoons at a time into egg mixture, while using the other hand to whisk the egg mixture continuously when combining the two mixtures.
Once the two mixtures are combine, pour it back into the pot and heat under medium heat until mixture comes to a boil. Whisk continuously!
Turn off heat, add mashed bananas and sweetened condense milk to pudding. Mix to combine.
Transfer pudding to a separate container, let it cool in room temperature for 30 minutes, then refrigerate for at least 3-4 hours until pudding is cold.
To make homemade whipped cream, whisk together heavy whipping cream and sugar under high speed using a stand mixer or hand held mixture, until whipped cream is thickened and no longer in liquid form. This will take at least a few minutes. Store whipped cream in refrigerator until pudding is cold. Alternatively, use store-bought cool whip and skip the homemade whipped cream step!
Layer pudding, sliced bananas, Nilla wafers, whipped cream/ cool whip onto a jar, bowl, or mug. Repeat to add another layer. Then top with a slice of banana and Nilla wafer.
Repeat Step 8 to fill up three more jars.
Let pudding sit for ~30 minutes so that Nilla wafers soften. Then serve and enjoy!
Want to make more than 4 servings? Spread everything out to 6-8 small jars and make smaller servings!