Place the egg yolk in a large mixing bowl and beat it lightly with a fork. Place the egg white in a medium mixing bowl and set aside.

In a large saucepan, make the hot cocoa mixture by whisking together the cocoa powder, 6 tablespoons sugar, cornstarch, and salt. Gradually whisk in the milk. Place over medium heat and bring to a boil. Boil gently, stirring constantly, for 1 minute.

Gradually pour some of this hot cocoa mixture into the bowl containing the egg yolk and whisk well. Add the rest of the hot cocoa mixture gradually, whisking constantly. Add the chocolate chips and whisk until they are all melted. Whisk in 1½ teaspoons of the vanilla.

Strain the mixture into a bowl or pitcher and divide among 6 cups or dessert bowls. Let cool, then top with plastic wrap pressed directly on the surface to prevent a skin from forming. Refrigerate until cold, at least 2 hours.

While the pudding is chilling, prepare the meringue marshmallows.

Preheat the oven to 400 degrees. Line a flat tray suitable to go in the microwave with a piece of parchment paper. If you don’t possess such a thing, you can use a small cutting board or flip over a Pyrex baking dish.

Beat the reserved egg white with an electric mixer until foamy. Gradually add the remaining 2 tablespoons sugar and beat until stiff peaks form. Add the remaining ¼ teaspoon vanilla and beat in.

Spoon the mixture into a small plastic food storage bag and snip off half an inch from one of the bottom corners. Pipe the meringue onto the prepared tray in 12 (1-inch) squares. Moisten your finger with a bit of water and gently push down any little peaks. Place the meringues in the microwave and cook on highest power for 30 seconds. Remove the meringues from the microwave, dust generously with the powdered sugar and transfer parchment paper holding the meringues onto a baking sheet. Cook for 4 minutes or until lightly golden brown. The meringue should feel crispy on the outside but soft and marshmallow-like in the center. Let cool completely. Can be made an hour or two ahead.

To serve, take the puddings out of the fridge for a few minutes to take the chill off. Gently slide the meringues off the parchment paper using a spatula and top each pudding with two meringues.