Scald milk, in a large sauce pot, with a pinch of the sugar (this avoids scorching the bottom of the pot).
In a mixing bowl, add egg yolks, banana extract, bourbon and 2 cups of sugar and whisk together until the mixture is pale yellow in color and thickened. Add cornstarch and mix to combine. Very slowly pour in a little of the milk mixture, you have to do it slowly to temper the mixture. Once fully incorporated pour the entire mixture back into the pot and place over medium heat. Stir constantly until it comes to a simmer and the mixture thickens enough that it coats the back of a wooden spoon. Remove from heat and add a pinch of salt and vanilla extract, then add butter cubes and stir to make the mixture rich and super glossy.Transfer to a bowl and cover with plastic wrap, pressing the wrap onto the surface so it doesn't form a skin on the surface. Allow to cool.
In a large bowl, using a hand mixer, whip the cream with 1/4 cup of sugar and a splash of vanilla extract until you have stiff peaks. Set aside.Slice bananas and add to pastry cream.Line a small deep rectangular dish or a 10-inch pie dish with vanilla wafers. Splash with more creme de banana then cover with banana pastry cream. Top with whipped cream and refrigerate until ready to serve.
Roll out pastry to fit a 9-in. pie plate. Transfer to pie plate; trim to 1/2 in. beyond edge of plate. Flute edges. Line unpricked pastry with a double thickness of heavy-duty foil. Bake at 450° for 8 minutes. Remove foil; bake 5-7 minutes longer or until golden brown. Cool on a wire rack.
In a large heavy saucepan, combine sugar and cornstarch. Gradually stir in milk and lemon juice; add egg yolks and lemon peel. Cook and stir over medium heat until thickened. Stir in butter and cool to room temperature. Stir in sour cream and pour filling into pie shell. Top with whipped cream. Store in the refrigerator.