1cupsugarincrease sugar to 1¼ cup if using dark chocolate
1 14.4ouncebox graham crackers3 individual packs or about 27 cracker sheets
In a medium saucepan combine the sugar, cornstarch, salt, and cocoa. Gradually stir in milk. Cook and stir the mixture until thickened and bubbly. Reduce heat; cook and stir 2 minutes more. Remove the saucepan from heat.
Meanwhile, line the bottom of a 13x9-inch baking dish with one pack of the graham crackers.
Separate egg yolks from egg whites. Beat egg yolks slightly. Quickly stir in 1 cup of the hot mixture into yolks (do this quick--the hot mixture can partially cook the eggs and leave egg pieces in the mixture). Return egg mixture to saucepan; bring to gentle boil. Cook and stir 2 minutes more. Remove from heat. Stir in butter and vanilla.
Working quickly, cover the graham crackers with a layer of custard; add a second layer of crackers and cover with custard; add the final layer of crackers and cover with remaining custard. Let cake cool to room temperature. Refrigerate overnight.
To save time, prepare two packages of cook and serve chocolate pudding (4.6 ounces each) and quickly alternate with one 14.4 ounce box of graham crackers. Refrigerate overnight.