Mix cocoa, cornstarch, beaten egg yolks; sugar and salt, then add milk gradually, while stirring in a pot over med-high heat. Cook until thick, beating it smooth. Cream pies take some time to thicken, so stir… and stir (10-15 min). Using a heavy bottom pan really helps. Just keep it up until it thickens.
Pour into a pre-baked pie shell. Put in the fridge to chill, add whipped cream if you like, Or use the left over egg whites for a meringue topping!