In a saucepan over medium heat, whisk together milk, heavy cream, sugar, egg yolks, and cornstarch. Cook while whisking constantly until the mixture thickens into a smooth custard. Remove from heat and stir in vanilla extract. Let cool slightly.

Using a small knife, cut a pocket or slit into the side or top of each Hawaiian roll without cutting all the way through.

Spoon or pipe the custard generously into each roll until filled. Arrange the stuffed rolls on a serving plate or baking dish.

Heat the heavy cream until just warm (not boiling). Pour over chocolate chips and let sit for 1 minute, then stir until smooth and glossy.

Spoon the chocolate ganache over the tops of the rolls. Garnish if desired. Refrigerate for at least 30 minutes to set before serving.