Gather the ingredients.
Blend the sugar, cornstarch, flour, salt, and 1 cup of milk together with a wire whisk.
Whisk in the remaining 2 cups of milk.
Cook over medium heat for 8 to 9 minutes, until the mixture thickens, stirring it constantly.
Remove from the heat and whisk in the egg yolks.
Return to medium heat and cook, stirring the mixture constantly for 2 to 3 minutes more.
Remove from the heat and stir in the chocolate squares, butter, and the vanilla. Stir until smooth and all the chocolate is melted.
Cool for 5 to 10 minutes, stirring occasionally. Pour into graham cracker pie and shell refrigerate for 4 hours. Make the Topping
Gather the ingredients.
Beat the whipping cream until soft peaks form.
Add the sugar slowly and beat until stiff peaks form.
Spread onto the cooled pie.
Sprinkle with ½ teaspoon of Hershey’s cocoa and serve.
