Step 1: Make the Graham Cracker Crust
Preheat oven to 325°F (163°C).
In a medium bowl, combine graham cracker crumbs, sugar, and melted butter. Stir until the mixture resembles wet sand.
Press the crust into the bottom of a 9-inch springform pan. Use a flat-bottomed glass to press evenly.
Bake for 10 minutes. Remove from oven and let cool while preparing the filling.

Step 2: Prepare the Cheesecake Layer
In a large bowl, beat the softened cream cheese until smooth and creamy.
Add sugar and mix until well incorporated.
Add eggs, one at a time, mixing on low speed after each addition.
Blend in vanilla extract, sour cream, and heavy cream until smooth and creamy.
Pour the cheesecake mixture over the cooled crust and smooth the top with a spatula.
Bake for 50-60 minutes or until the center is just set but slightly jiggly.
Turn off the oven, crack the door, and let the cheesecake cool inside for 1 hour.
Transfer to the fridge and chill for at least 4 hours, preferably overnight.

Step 3: Make the Pastry Cream Layer
In a medium saucepan, heat milk over medium heat until just beginning to steam.
In a separate bowl, whisk together sugar, egg yolks, and cornstarch until smooth.
Slowly pour the hot milk into the yolk mixture, whisking constantly to prevent scrambling.
Return the mixture to the saucepan and cook over medium heat, stirring constantly until thickened, about 5-7 minutes.
Remove from heat and stir in butter and vanilla.
Pour pastry cream through a sieve into a bowl for an extra smooth finish (optional).
Cover with plastic wrap pressed directly on the surface and refrigerate until fully chilled.

Step 4: Layer the Pastry Cream
Once the cheesecake is fully chilled and firm, spread the cooled pastry cream evenly over the top using an offset spatula.
Chill in the refrigerator for at least 1 hour to set the cream layer.

Step 5: Make the Chocolate Ganache
In a small saucepan, heat the heavy cream until just simmering.
Pour over chopped chocolate in a bowl. Let sit for 2 minutes, then stir until smooth and glossy. Add corn syrup for added shine, if desired.
Let ganache cool for 5-10 minutes, then gently pour over the pastry cream layer.
Tilt the pan gently to evenly spread the ganache.
Refrigerate for another hour, or until the ganache is set.

Step 6: Serve and Enjoy
Carefully remove the springform ring.
Slice with a hot knife for clean cuts, wiping the blade between slices.
Serve chilled and enjoy the layers of creamy, chocolaty, custard-filled goodness.