In a medium bowl, add the sugar, cornstarch and salt and whisk until completely combined. Whisk in the milk and egg yolks, ensuring everything is completely incorporated.
Transfer the mixture to a medium saucepan then rinse and dry the mixing bowl. Set a strainer over the mixing bowl and set aside.
Place the saucepan over medium heat and stir the mixture constantly until it begins to bubble then reduce heat to low and continue stirring for 1 full minute.
Once the mixture has thickened and cooked at a simmer for 1 minute, pour the mixture through the strainer set over the mixing bowl—be sure to press all of it through the strainer and scrape the bottom to get as much as possible.
Whisk in the butter and vanilla while the mixture’s still hot. Make sure everything is combined and the butter has completely melted.
Add sliced bananas to the bottom of pre-baked pie shell. Pour filling on top of bananas then spread evenly.
Cover with plastic wrap so the plastic is touching the pie filling. This will prevent a skin from forming.
Chill for 3-4 hours until completely cooled then top with whipped cream, additional banana slices and serve!
Whisk all ingredients together first then place over heat and keep stirring so there’s no curdling.