Graham Cracker Crust: In small bowl, combine graham cracker crumbs, sugar and butter. Press evenly on bottom and sides of 9-inch pie plate. Chill until firm (about 1 hour).
Chocolate Layer: In medium saucepan, combine sugar, cornstarch and salt. Gradually stir in milk. Cook over medium heat, stirring constantly, until mixture boils. Remove from heat. In small bowl, beat egg yolks. Gradually stir in small amount of hot mixture; return to saucepan. Cook over low heat, stirring constantly, for 2 minutes. Remove from heat.
Remove 1-1/2 cups custard to medium bowl; add semi-sweet chocolate morsels and vanilla extract. Stir until morsels are melted and mixture is smooth.
Pour into prepared Graham Cracker Crust; chill until set (about 30 minutes).
While Chocolate Layer is chilling, prepare Vanilla Layer.
Vanilla Layer: In large bowl, combine cold water and gelatin; let stand 5 minutes. Add remaining warm custard; stir until gelatin dissolves. Cool 15 minutes. Stir in rum; beat with wire whisk until smooth. Set aside.
In 1-1/2 quart bowl, combine egg whites and cream of tartar; beat until foamy. Gradually add sugar; beat until stiff peaks form. Fold egg whites into custard; pour over chocolate layer.
Chill until set (about 2 hours).
Garnish with whipped cream and chocolate shavings, if desired.