Prepare and bake Pastry Crust in a 9-inch pie plate. Cool completely on a wire rack.
Combine 1 tablespoon cornstarch, 2 tablespoons sugar, cocoa, and dash of salt in a small, heavy saucepan; gradually add 1/3 cup milk, stirring with a whisk. Cook 2 minutes over medium-low heat. Stir in chocolate; bring to a boil over medium heat. Reduce heat to low; cook 1 minute, stirring constantly. Spread chocolate mixture into bottom of prepared crust.
Combine 2 tablespoons cornstarch, 1/2 cup sugar, 1/4 teaspoon salt, eggs, 1 cup milk, and margarine in a heavy saucepan over medium heat, stirring constantly with a whisk. Bring to a boil. Reduce heat to low, and cook 30 seconds or until thick. Remove from heat. Add vanilla. Beat cream cheese until light (about 30 seconds). Add 1/4 cup hot custard to cream cheese, and beat just until blended. Stir in remaining custard.
Arrange banana slices on top of chocolate layer; spoon custard over bananas. Press plastic wrap onto surface of custard; chill 4 hours. Remove plastic wrap. Spread whipped topping evenly over custard. Garnish with chocolate curls, if desired. Chill until ready to serve.