01 - Whisk together sugar, cocoa powder, cornstarch, and salt in a medium saucepan until evenly blended.
02 - Gradually whisk in the milk and cream, stirring continuously until smooth and no lumps remain.
03 - Place saucepan over medium heat. Cook while whisking constantly until mixture thickens and begins to bubble, approximately 5–7 minutes.
04 - Reduce heat to low. Add chopped chocolate and butter, whisking until completely melted and incorporated.
05 - Remove from heat. Stir in vanilla extract until fully combined.
06 - Pour pudding into individual serving dishes. Press plastic wrap directly onto surface of each to prevent skin formation.
07 - Refrigerate for at least 45 minutes for chilled pudding, or serve immediately if warm texture is preferred.