01 -
In a large saucepan, whisk together sugar, cornstarch, and milk until smooth. Cook over medium heat, stirring constantly, until the mixture thickens and starts to bubble. Let it simmer for 1 minute, then remove from heat.
02 -
Slowly whisk a small amount of the hot milk mixture into the egg yolks to warm them up. Then pour this egg mixture back into the saucepan, whisking constantly to prevent scrambling.
03 -
Return the pan to medium heat and bring to a gentle boil. Cook for 2 minutes, stirring continuously. Remove from heat and stir in butter and vanilla until smooth. Let cool to room temperature.
04 -
Preheat oven to 350°F and line two 12-cup muffin tins with paper liners. Mix cake mix, water, melted butter, and eggs until just combined. Fill liners halfway and bake for 15 minutes until a toothpick comes out clean. Cool completely.
05 -
Combine chocolate chips and heavy cream in a microwave-safe bowl. Heat in 15-second intervals until chocolate melts completely. Sift in powdered sugar and let cool for 10 minutes until it thickens.
06 -
Use a knife to cut out the center of each cupcake about 1 inch wide and 1 inch deep. Fill each hollow with pastry cream using a piping bag or spoon. Top each cupcake with a generous dollop of chocolate ganache.