Dissolve in Jello in the boiling water.Add the 7-Up to the Jello and let set until slightly thickened in fridge. (I think I waited 20-30 minutes)Fold the bananas, marshmallows, and pineapple into the thickened Jello and pour into a 9 x 13 pan. Place in the fridge and let the Jello set completely while you prepare the topping.In a sauce pan, combine the reserved pineapple juice, egg, sugar, and cornstarch. Mix and bring to a boil, stirring constantly. Cook until thick. Allow mixture to cool.Fold whipping cream into the cooled juice mixture and spread on top of set Jell-0.