01 - In a medium saucepan, whisk together sugar, cocoa powder, cornstarch, and salt. Gradually add milk while whisking to dissolve all dry ingredients.
02 - Place saucepan over medium heat. Cook, whisking constantly, until mixture thickens and starts to bubble, about 5 to 7 minutes.
03 - Remove from heat. Stir in chopped chocolate and vanilla extract until chocolate melts and pudding is smooth.
04 - Pour pudding into 4 serving dishes. Cool slightly, then cover surface with plastic wrap to prevent skin formation. Refrigerate for at least 1 hour until fully chilled.
05 - In a chilled bowl, beat heavy cream, powdered sugar, and vanilla extract until soft peaks form.
06 - Top each chilled pudding with a generous dollop of whipped cream before serving.