In a medium-sized bowl add the sugar, flour, and unsweetened cocoa and whisk together.
Pour in the milk, vanilla extract, and egg yolks (save the whites in another bowl). Beat with a hand mixer until well combined.
Add the butter to a skillet on medium heat.
Next, pour the chocolate pie filling into the pan and cook until thick.
Pour the pie filling back into a clean (and heat-safe) bowl and beat again to get rid of any lumps.
Pour the filling into the cooked pie shell.
Meringue
Grab the bowl with the whites and add one more egg white.
Add the cream of tartar to the bowl and beat until stiff peaks form.
Pour the sugar into the bowl and beat again until the meringue is shiny.
Spread the meringue over the pie. Bake at 350-degrees for about 10-15 minutes or until the meringue is golden brown.
Allow the pie to set up for at least one hour before serving.
Video
Notes
TIP: Make sure the bowl and beaters are dry before beating the egg whites. If you have any water or egg yolks in the bowl or on the beaters the meringue will not fluff up. TIP: The chocolate filling will thicken fast when cooking, so don't go to far.