01 - Whisk together granulated sugar, unsweetened cocoa powder, cornstarch, and salt in a medium saucepan.
02 - Gradually whisk in whole milk and heavy cream until the mixture is smooth.
03 - Place saucepan over medium heat, stirring constantly until the mixture thickens and reaches a gentle boil, about 5 to 7 minutes.
04 - Reduce heat to low and continue stirring for an additional 2 minutes.
05 - Remove from heat, then stir in finely chopped chocolate and unsalted butter until fully melted and combined.
06 - Mix in pure vanilla extract to enhance flavor.
07 - Pour pudding evenly into serving dishes.
08 - Cover each dish with plastic wrap pressed directly onto the pudding surface.
09 - Refrigerate for at least 40 minutes before serving to set.