01 - In a medium saucepan, whisk together sugar, cocoa powder, cornstarch, and salt until evenly incorporated.
02 - Gradually whisk in the whole milk and heavy cream until the mixture is smooth and free of lumps.
03 - Place the saucepan over medium heat and cook, whisking constantly, until the mixture thickens and begins to bubble, about 6 to 8 minutes.
04 - Remove from heat and immediately add the chopped dark chocolate, stirring until fully melted and the mixture is smooth.
05 - Stir in the pure vanilla extract until evenly distributed.
06 - Pour the hot pudding into individual ramekins or serving dishes.
07 - Cover the surface of each pudding with plastic wrap to prevent a skin from forming.
08 - Refrigerate for at least 2 hours until fully chilled and set.
09 - Serve plain or topped with whipped cream or chocolate shavings, if desired.