Heat the milk in a medium-sized pot over medium heat.
Meanwhile, in a bowl, combine the sugar, flour, salt, and cocoa.
Add the dry mixture to the milk and cook until thickened, stirring constantly.
Temper the eggs by adding a small amount of the hot milk mixture into the beaten egg yolks and stir. Pour the egg yolk mixture back into the pot, stirring constantly.
Cook the pudding for at least two minutes.
Stir in the vanilla and pour the pudding into the pie shell.
When the chocolate base cools, you can top with Cool Whip or whipped cream.
