Prepare the Cheesecake Crust:

• Preheat the oven to 325°F (165°C).
• In a bowl, mix the graham cracker crumbs, sugar, and melted butter until combined. Press this mixture into the bottom of a 9-inch springform pan to form a crust. Bake for 10 minutes, then remove from the oven and set aside to cool.

Make the Cheesecake Filling:

• In a large bowl, beat the cream cheese with a hand mixer or stand mixer until smooth and creamy.
• Add the sour cream, sugar, eggs (one at a time), vanilla extract, and flour. Mix until smooth and combined.
• Pour the cheesecake batter over the cooled crust and smooth the top.
• Bake for 50-55 minutes, or until the edges are set but the center still slightly jiggles.
• Turn off the oven and let the cheesecake cool inside for 1 hour. Then, transfer it to the fridge and chill for at least 4 hours or overnight.

Make the Vanilla Custard Layer:

• In a medium saucepan, heat the milk and sugar over medium heat until warm.
• In a separate bowl, whisk together the egg yolks and cornstarch. Gradually pour the warm milk mixture into the egg yolk mixture, whisking constantly to prevent curdling.
• Pour the combined mixture back into the saucepan and cook over medium heat, whisking constantly until the custard thickens. This will take about 5-7 minutes.
• Remove from heat and stir in the butter and vanilla extract. Let the custard cool to room temperature before spreading it over the cheesecake.

Prepare the Chocolate Ganache:

• In a small saucepan, heat the heavy cream over medium heat until it just starts to simmer.
• Pour the hot cream over the chopped chocolate in a heatproof bowl. Let it sit for 2-3 minutes, then stir until smooth.
• Add the butter and stir until fully combined and glossy.

Assemble the Boston Cream Pie Cheesecake:

• Once the cheesecake has cooled and chilled, spread the vanilla custard layer evenly over the top of the cheesecake.
• Pour the chocolate ganache over the custard layer and spread it out evenly.
• Return the cheesecake to the fridge to chill for an additional 1-2 hours until the ganache is set.

Serve:

• Once everything is set, remove the cheesecake from the springform pan and transfer it to a serving platter. Slice and enjoy!