I start by heating milk in a saucepan until warm but not boiling. In a bowl, I whisk egg yolks, sugar, and cornstarch until smooth. Then I slowly combine everything and cook until thick and creamy.
Once the custard thickens, I remove it from heat immediately. I stir in butter and vanilla extract for a silky smooth finish. Then I let it cool completely so it doesn’t melt the rolls later.
I carefully slice each Hawaiian roll without cutting them fully apart. I gently create a pocket inside each roll for the filling. This helps hold the custard without breaking the soft structure.
I spoon the cooled custard into each roll generously and evenly. I make sure every roll is filled to the center for balance. Then I place them neatly on a serving tray for the topping step.
I heat heavy cream until warm and pour it over chocolate chips. After a minute, I stir until the mixture becomes smooth and glossy. This creates that classic Boston cream pie chocolate finish.
I drizzle the chocolate ganache over the stuffed rolls evenly. Then I let them chill for at least 15 minutes before serving. This helps everything set and makes the texture even better.