For The Crust
Butter 9 -inch glass pie dish. In a heavy, small saucepan stir butter and chocolate over low heat. Mix in cookie crumbs. Press unto bottom and sides. Chill until firm (about 30 minutes).
For Chocolate Ganache
In a medium saucepan over medium heat, heat butter and cream until hot, but do not boil. Remove from heat and add chocolate and vanilla. Whisk until smooth. Reserve 2 tablespoons of the ganache in a small bowl at room temperature (to be used as garnish). Pour remaining ganache over crust. Chill crust until chocolate ganache is firm (about 30 minutes).
Thinly slice 3 bananas. Arrange banana slices over chocolate. Whisk Vanilla Pastry Cream until smooth. Spread pastry cream evenly over bananas. Drizzle reserved chocolate ganache over pastry cream. Draw toothpick through pastry cream and chocolate to marbleize. Refrigerate until pastry cream is set (at least 3 hours and up to one day).
Spoon vanilla whipped cream around edges of pie or decoratively pipe cream with pastry bag. Slice remaining banana. Garnish banana with pie slices.
Vanilla Pastry Cream
In a heavy medium saucepan, bring half and half to a a simmer. In a medium bowl, whisk sugar, eggs, egg yolk and flour in medium bowl to blend. Gradually whisk in hot half and half. Transfer to saucepan. Whisk over medium heat until mixture thickens and comes to a boil (about 5 minutes). Boil 1 minute. Pour into a medium bowl. Stir in vanilla. Press plastic unto surface of cream. Cover; chill until cold (about 4 hours).
Vanilla Whipped Cream
In a medium bowl, beat cream, powders sugar and vanilla extract until peaks form. Can be made 4 hours ahead.