01 - Whisk together sugar, 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 the saucepan over medium heat, stirring constantly until the mixture thickens and reaches a gentle boil, approximately 5 to 7 minutes.
04 - Lower the heat to low and continue cooking for 2 minutes, stirring continuously.
05 - Remove from heat; stir in chopped chocolate and unsalted butter until fully melted and smooth.
06 - Incorporate vanilla extract and mix thoroughly.
07 - Divide the pudding evenly into individual serving dishes.
08 - Cover each dish with plastic wrap, pressing the wrap directly onto the pudding surface.
09 - Refrigerate for at least 40 minutes to allow the pudding to set before serving.