Start by preparing your pie crust. Press the crust along the bottom and edges of your pie plate. Crimp the edges. Using a fork, poke the bottom of the crust generously. This prevents it from puffing up during baking. Bake your crust at 450 for 8-10 minutes until golden. This technique is called a blind bake. You can cover your crust with parchment and fill with beans to ensure the shape remains, but it is not necessary. Once crust is baked, set aside to cool.
In a medium mixing bowl, add eggs. Whisk until smooth and set aside.
In a 4 quart saucepan, add your sugar, cornstarch, and salt. Whisk to combine these dry ingredients.
Pour in whole milk and half and half. Whisk until well combined. Set heat on your stove to medium.
As you heat the mixture continually whisk. When I say continually, I mean constantly. You're going to stir until your arms fall off. Stir continuously until mixture is thickened and simmering. You want the temperature of the mixture to be between 175-180 degrees Fahrenheit. This will take roughly 10-15 minutes. Make sure you are stirring the entire time.
You'll know when the mixture is thick enough because you'll be able to coat the back of a wooden spoon and run your finger through it. If the line remains, it is thick enough.
Add about a cup of hot liquid to your slightly beaten eggs, adding 1 tablespoon at a time. Make sure you are whisking eggs continuously while you pour the small amount of hot liquid in. This is called tempering your eggs.
Pour tempered eggs into your thickened custard while you whisk. Continue to stir and cook for an additional 2-3 minutes.
Remove from heat and add in butter and vanilla. Stir until combined and smooth.
Line pie crust with slices of 2 bananas.
Pour custard on top of banana layer.
Press plastic wrap to the surface of the custard layer. This prevents the custard from forming a thick skin. Cool and refrigerate overnight.
Top with whipped cream, and additional banana slices if desired. Serve chilled.