For extra chocolate flavor, use grated bittersweet chocolate for the sprinkles.
For pastry crusts, in a large bowl stir together flour, cocoa, and salt. Using a pastry blender, cut in shortening and 1/3 cup butter until pieces are pea-size. Sprinkle 1 tablespoon water over flour mixture; gently toss with a fork. Push moistened dough to side of bowl. Repeat, using 1 tablespoon water at a time, until all flour is moistened and dough is formed.
Preheat oven to 450° F. Divide dough in half. Form each half in a ball. Cover and refrigerate one ball. On lightly floured surface, flatten remaining ball. Roll from center to a 12-inch circle. Transfer to 9-inch pie plate. Gently fit into plate, avoiding stretching crust. Trim crust along pie plate edges. Line crust with a double thickness of foil.
Bake pastry for 8 minutes. Remove foil; bake 5 minutes more, until dry. Sprinkle with chocolate chips. Cool completely on wire rack. Reduce oven to 325° F.
For chocolate filling, in a 2-quart saucepan stir together sugar and cornstarch. Stir in milk and unsweetened chocolate. Cook and stir over medium heat until thickened and bubbly. Cook and stir 2 minutes more.
Slowly stir 1 cup of the hot chocolate into the beaten egg yolks. Pour chocolate-egg mixture into hot filling in pan. Bring just to boiling; reduce heat. Cook and stir for 2 minutes. Remove from heat. Stir in butter and vanilla. Cool 10 minutes.
Meanwhile, on a lightly floured surface, flatten chilled dough. Roll from center to edges to 12-inch circle. Pour warm filling into baked pastry shell. Place unbaked pastry over filling, pressing edges to seal (see Tip below). Trim pastry to edge of pie plate. Gently prick top pastry with a fork. Bake for 25 minutes, until crust is firm and dry. Cool 1 hour on wire rack.
To serve, invert a serving platter on pie. Turn pie and platter upside down. Remove pie plate. Top with sweetened whipped cream, sliced bananas, maraschino cherries, and some of the Easy Fudge Sauce. Or, to serve just a few slices, top each slice wit the whipped cream and toppings. Cover and refrigerate remaining pie up to 2 days. Individual slices can be reheated in a microwave for 10 to 15 seconds.
For extra chocolate flavor, grate a chocolate bar over the top before serving.
After rolling the top pastry, wrap it around a rolling pin. Transfer to pie and carefully unroll, avoiding stretching the pastry. Use a small knife to trim pastry even with pie plate, then press top and bottom crust edges together to seal.