For crust:- combine crushed cereal with melted butter and press into the bottom and sides of a pie dish. Bake in a preheated oven at 350° (180°C) for 10 minutes, then allow to cool completely.
For filling:- in a medium heavy bottom saucepan, combine thoroughly the sugar, cornstarch and salt. Then add the Evaporated Milk, egg yolks and cocoa powder and whisk to incorporate.
Constantly stirring over medium heat until the mixture thickens into a pudding consistency.
Remove from heat and mix in the vanilla essence and butter.
Pour mixture into the cooled pie crust and place in the refrigerator for a few hours to set.
Top with whipped cream before serving.