How to Make It
In a medium saucepan, whisk the cream with the milk and the egg. In a medium bowl, whisk the sugar with the cocoa, cornstarch and salt. Add to the saucepan and bring to a boil over moderately high heat, whisking constantly. Strain the pudding into a medium bowl. Stir in the butter and chocolate until melted.
To cool the pudding, pour it into a large glass baking dish. Press plastic wrap directly on the surface of the pudding and refrigerate for 30 minutes, or until chilled.
Spoon the pudding into bowls, top with whipped cream and serve.