In a medium size bowl, whisk together the egg yolks, cocoa, salt and cornstarch.

Pour milk in a medium saucepan, and bring to a boil.

Once milk is at a boil, take off heat and add a little bit at a time into the egg mixture.

Pour the mixture into another CLEAN (this is important - you do not want to scorch!) medium saucepan and add vanilla.

Whisk until it starts to thicken up, about 4 minutes.

Keep on whisking until the pudding is thick and glossy for about another 2 minutes.

Transfer the pudding to a clean bowl and incorporate the chocolate and butter and whisk together until incorporated.

Refrigerate for about an hour then divide the pudding into mini cups or bowls and serve.

Will keep for about 5 days in the refrigerator covered in plastic wrap.