Heat oven to 375°. Break graham crackers into food processor and run until fine crumbs are formed. Transfer crumbs to a bowl and mix in brown sugar and melted butter. Press mixture evenly into a 9-inch pie plate. Bake at 375° for 8 to 10 minutes or until crust is slightly brown. Cool 10 minutes.
Reduce oven to 325°. Beat eggs in a small bowl; set aside. Combine milk, cream, sugar and salt in a medium saucepan over medium heat until simmering. Remove from heat and add vanilla, chocolate and cocoa powder; stir until combined and smooth. Stir about 3/4 cup of the chocolate mixture into the beaten eggs; stir chocolate-egg mixture back into saucepan. Pour filling into cooled crust. Bake at 325° for 25 to 30 minutes, or until the filling is set and glossy (do not over-bake or it could bubble and crack). Cool completely on a wire rack.
Bring 1 inch of water to a simmer in a medium saucepan. Combine egg whites, corn syrup, sugar and salt in a metal bowl large enough to sit on top of the saucepan. Whisk constantly in bowl over water until sugar is dissolved and eggs have reached 160°, about 3 to 5 minutes (do not overcook, as the eggs could scramble). Pour mixture and vanilla into the bowl of a stand mixer fitted with a whisk and beat on high speed until fluffy, about 5 minutes. Set aside.
Heat broiler. Spoon Marshmallow Topping on cooled pie, leaving a 1-inch margin from edge. Broil until topping begins to brown, 1 minute.