Prebake your preferred crust at 425 degrees. I prick the crust with a fork, add parchment paper and pie weights. Cook for 10-12 minutes until browned. I used a store bought Pillsbury pie crust that worked perfectly.
Combine the sugar, flour, salt and cocoa in a sauce pan. Bring water to a boil and while whisking, add to the dry ingredients, continuing to whisk to prevent lumps.
Temper the eggs by adding a little of the hot pudding to them and combining, then add to the custard. Continue to cook until thick. Remove from the heat and add the butter. I refrigerated mine before adding to the cooled crust.
Beat the egg whites, while adding a little sugar at a time, along with the vanilla until stiff peaks form.
Spread on the pie and bake for a few minutes at 450 degrees until lightly browned. Cool before cutting.