This was passed on to me by my sister, who I'm sure found it in a magazine, probably Southern Living, although I'm not sure where she got it. Cooking time includes the chilling time. Actual cooking time is about 35 to 45 minutes.
To prepare the crust, reserve 1 tablespoon crumbs for topping. Combine the remaining crumbs, 2 tablespoons sugar, cinnamon, and 1/8 teaspoon salt in a bowl, stirring well. Stir in egg white and butter. Press crumb mixture into bottom and up sides of a 9-inch pie plate coated with cooking spray.
Bake at 375° for 9 minutes or until lightly toasted; cool completely on a wire rack.
To prepare filling, combine 1/2 cup sugar and the next 7 ingredients (through egg yolk) in a bowl, stirring well with a whisk.
Place the milk in a medium, heavy saucepan over medium-high heat; cook until milk reaches 180° or until tiny bubbles form around edge (do not boil). Gradually add hot milk to egg mixture, stirring constantly with a whisk. Return milk mixture to pan; cook over medium heat 10 minutes or until thick and bubbly, stirring constantly. Remove from heat. Add chocolate; stir until smooth.
Place pan in a large ice-filled bowl for 10 minutes or until mixture cools, stirring occasionally. Spoon filling into crust, and cover surface of filling with plastic wrap. Chill for 3 hours or until set; remove plastic wrap. Spread the whipped topping over filling; sprinkle with reserved cracker crumbs.