Prepare the Crust: Preheat oven to 325°F (163°C). Mix graham cracker crumbs, sugar, and melted butter in a bowl. Press into the bottom of a 9-inch springform pan. Bake for 10 minutes, then let cool.

Make the Cheesecake Layer: In a large bowl, beat cream cheese and sugar until smooth. Add eggs one at a time, mixing well. Stir in vanilla extract and heavy cream. Pour over the crust. Bake for 45-50 minutes, until the center is set. Let cool completely.

Prepare the Pastry Cream: In a saucepan over medium heat, heat milk until warm. In a bowl, whisk sugar, egg yolks, and cornstarch until smooth. Gradually add warm milk, whisking constantly. Return the mixture to the saucepan and cook until thickened, stirring continuously. Remove from heat, add vanilla and butter, and let cool. Spread over the cooled cheesecake.

Make the Chocolate Ganache: Heat heavy cream until steaming but not boiling. Pour over chocolate chips and let sit for 2 minutes. Stir until smooth, then add vanilla extract. Let cool slightly before pouring over the pastry cream layer.

Chill and Serve: Refrigerate for at least 4 hours or overnight before slicing and serving.