Step 1: Prepare the Crust
Preheat the oven to 325°F (160°C).
Mix graham cracker crumbs, sugar, and melted butter in a bowl until evenly combined.
Press the mixture firmly into the bottom of a 9-inch springform pan.
Bake for 10 minutes. Let it cool while preparing the cheesecake.

Step 2: Make the Cheesecake Filling
In a large bowl, beat the softened cream cheese until smooth.
Add sugar and mix until light and fluffy.
Beat in eggs one at a time, scraping down the bowl as needed.
Add vanilla extract, sour cream, heavy cream, and flour. Mix just until combined—don’t overbeat.

Step 3: Bake the Cheesecake
Pour the cheesecake filling over the cooled crust.
Wrap the pan in foil and place it in a larger roasting pan. Fill the outer pan with about 1 inch of hot water to create a water bath.
Bake at 325°F for 55–65 minutes, or until the center is just set and slightly jiggly.
Turn off the oven and crack the door. Let the cheesecake cool in the oven for 1 hour.
Remove from the oven and chill in the refrigerator for at least 4 hours or overnight.

Step 4: Make the Custard Layer
In a medium saucepan, whisk together milk, sugar, and cornstarch.
In a separate bowl, whisk the egg yolks.
Gradually add a bit of the hot milk mixture to the yolks to temper them, then pour back into the saucepan.
Cook over medium heat, whisking constantly, until the mixture thickens (about 5–7 minutes).
Remove from heat, stir in butter and vanilla.
Cool to room temperature, then refrigerate until ready to use.

Step 5: Make the Chocolate Ganache
Place chocolate chips in a heatproof bowl.
Heat heavy cream in a small saucepan until it just begins to simmer.
Pour the hot cream over the chocolate and let sit for 2–3 minutes.
Stir until smooth, then add vanilla extract. Let cool slightly before pouring.

Step 6: Assemble the Cheesecake
Once the cheesecake is fully chilled, spread the pastry cream evenly over the top.
Pour the cooled ganache over the custard layer, gently spreading to the edges.
Chill for at least 1 hour to set the ganache before slicing and serving.

Step 7: Garnish & Serve
Slice the cheesecake with a hot, clean knife for neat pieces.
Optional: Garnish with chocolate shavings, whipped cream, or a cherry on top for a bakery-style finish.