Chocolate graham cracker crust: Mix everything together, press into bottom and sides of a 9-inch pie pan (you'll have some left over).
Bake at 350° for 12 minutes; set aside to cool.
Chocolate banana filling: In a medium saucepan, combine sugar, cornstarch and salt.
Stir in milk, blending well.
Cook over medium heat, stirring constantly, until mixture boils and thickens.
Boil 2 minutes.
Remove from heat.
Blend a small amount of hot mixture into egg yolks to temper them.
Return egg mixture to saucepan, blending thoroughly.
Cook until mixture just begins to bubble, stirring constantly.
Remove from heat; stir in butter, vanilla and chocolate.
Pour into cooled pie shell, top with banana slices and refrigerate.
Whipped topping: Whip until stiff, spread over filling and return pie to refrigerator for at least 2 more hours before serving.