To prepare crust, place crackers in a food processor; process until crumbly. Add 2 tablespoons sugar, butter, and egg white; pulse 6 times or just until moist. Press crumb mixture into a 9-inch pie plate coated with cooking spray. Bake at 350° for 8 minutes; cool on a wire rack 15 minutes.
To prepare filling, combine 1/2 cup milk, 2/3 cup sugar, and next 4 ingredients (2/3 cup sugar through egg) in a large bowl, stirring with a whisk.
Heat 1 1/2 cups milk in a heavy saucepan over medium-high heat to 180° or until tiny bubbles form around edge (do not boil). Remove from heat. Gradually add hot milk to sugar mixture, stirring constantly with a whisk. Return milk mixture to pan. Add chopped chocolate; cook over medium heat until thick and bubbly (about 5 minutes), stirring constantly. Reduce heat to low; cook 2 minutes, stirring constantly. Remove from heat; stir in vanilla. Pour into prepared crust; cover surface of filling with plastic wrap. Chill 3 hours or until cold. Remove plastic wrap; spread whipped topping evenly over filling. Sprinkle with grated chocolate.
Note: If you want to serve this with a dessert wine, try Thomas "Razz," nonvintage Washington State. It's made from raspberries, which go well with chocolate. If your wine shop doesn't carry it, ask them to order it for you.