Preheat your oven to 325°F (160°C). In a large bowl, combine the graham cracker crumbs, granulated sugar, and melted butter. Mix until it resembles wet sand. Press this mixture firmly into the bottom of a 9-inch springform pan. Bake the crust for about 10 minutes, then set aside to cool.

In a mixing bowl, combine the cream cheese and powdered sugar until smooth. Add the eggs one at a time, mixing well after each addition. Stir in the vanilla extract and heavy cream. Pour the batter over the cooled crust and smooth the top.

Bake for 50-60 minutes, or until the edges are set and the center has a slight jiggle. Turn off the oven, crack the door, and let the cheesecake cool down gradually.

In a saucepan, combine the milk, sugar, cornstarch, and egg yolks over medium heat. Whisk continuously until it thickens into custard, about 5-7 minutes. Add vanilla extract at the end and let cool slightly.

Microwave the heavy cream until hot but not boiling, then pour it over the chocolate chips in a bowl. Let it sit for a minute to melt the chocolate, then stir until smooth.

Once everything has cooled, spread the custard over the cheesecake, followed by a drizzle of chocolate ganache on top. Decorate with whipped cream or chocolate shavings.