In medium saucepan, heat 1 1/2 cups milk and 1/2 cup sugar over medium heat and bring to a boil.
In a bowl, stir together remaining 1/2 cup milk, remaining 1/4 cup sugar, egg yolks, flour, cornstarch, and salt. Using a whisk, stir together until completely smooth.
Temper the egg mixture by gradually adding a small amount of hot milk mixture to the bowl, whisking constantly. Add remaining mixture until it is all combined.
Return mixture to saucepan and cook over medium heat, stirring constantly, until mixture comes to a boil and begins to thicken and coats the back of a spoon, about 4-7 minutes.
As soon as the pastry cream thickens, remove from heat and add vanilla and butter.
Let chill on top of ice bath and then tightly cover.
Let chill in refrigerator for at least 1 hour to set up.
In a heavy bottomed saucepan, heat sugar and water over medium high heat, whisking constantly to dissolve sugar. Once mixture reaches a boil, stop whisking. Watch carefully as it transitions from white to light amber color. This is an important step to ensure that it doesn't burn. Once mixture reaches a medium amber color, add butter and whisk until butter is melted. If you own a candy thermometer, it usually turns the perfect amber color at approximately 250 degrees.
Once it's melted, immediately remove pan from heat. Wait 10 seconds and then add heavy cream. Whisk well to combine until glossy and smooth.Add salt. Allow caramel to cool for several minutes and then place in jar and place in the refrigerator to cool.
Whipping Cream:
Beat heavy cream until soft peaks form. Stir in powdered sugar.
Assemble Pie:
Bake pie crust according to recipe.
Cover the bottom of the prepared crust with sliced bananas and optional drizzle with 1/4 cup Salted Caramel Sauce. Top with half of vanilla pastry cream and bananas (sprinkle bananas with fruit fresh to keep from browning), covering the bananas completely. Repeat layering with the remaining bananas and the remaining custard. Drizzle with caramel sauce. Cover with whipped cream. Drizzle caramel sauce on top of the cream. Chill the banana cream pie until the filling is set, about 2 hours.
Notes
*Use fresh fruit or lemon juice on bananas to keep from browning.*The salted caramel can make the custard a little runny once it sits. If you want a firmer custard, only drizzle the caramel on the top of the pie.