In a saucepan over med heat combine all the ingredients for the filling except the vanilla and butter. (2 c evaporated milk, 1 c sugar, 1/4 c corn starch, 3 egg yolks, 1/2 c cocoa powder, 1/4 tsp salt)
Whisk together. Continue whisking till it comes to a boil and starts to thicken.
Once thickened, remove from heat, then add butter and vanilla. (1 tbs unsalted softened butter, 1 tsp pure vanilla extract)
Stir and pour into the pre-baked pie crust. (One 9 inch baked pie crust)
Cool, then chill in the refrigerator for several hours.
Top with whipped cream and chocolate shavings or with meringue, if desired. (Whipped cream, chocolate shavings or meringue, if desired)
