Step 1Sift together the cornstarch and sugar.
Step 2Combine the egg yolks and eggs in a separate bowl and set aside.
Step 3In a heavy bottomed saucepan combine the cornstarch and sugar. Stir in the milk and the vanilla bean with seeds. Heat the mixture to a simmer, stirring, and cook for 2 minutes, stirring constantly. Remove the vanilla bean.
Step 4Pour a little of the hot milk mixture into the eggs and whisk to combine. Return the egg-milk mixture to the saucepan and whisk to combine. Heat to a simmer again. Continue to cook over low heat until the mixture thickens, about 1 minute.
Step 5Remove from heat and whisk in the butter until it is fully incorporated and the mixture is smooth. Strain into a bowl, then cover the surface with plastic wrap. Cool completely in the refrigerator.
Step 1To make the filling, whip together the heavy cream and creme fraiche until soft peaks form. Stir the pastry cream until smooth. Fold one-half cup of the whipped cream into the pastry cream.
Step 2Line a baked graham cracker crust with one layer of sliced bananas. Reserve one-half banana to garnish the top, then fold the remaining banana slices into the filling.
Step 3Spoon the filling into the pie crust and top with the remaining whipped cream. Arrange the reserved banana slices on top. Serve chilled within 24 hours.