Step 1: Prepare the Crust
Preheat your oven to 325°F (160°C).
Mix graham cracker crumbs, sugar, and melted butter in a bowl.
Press the mixture firmly into the bottom of a greased 9-inch springform pan.
Bake for 8 minutes. Remove from oven and set aside to cool.

Step 2: Make the Cheesecake Layer
In a large bowl, beat the cream cheese and sugar until smooth and creamy.
Add the eggs one at a time, beating well after each addition.
Mix in vanilla extract and sour cream until just combined.
Pour the cheesecake batter over the cooled crust and smooth the top.

Step 3: Bake the Cheesecake
Bake the cheesecake for 50-55 minutes, until the center is just set and slightly wobbly.
Turn off the oven, crack the door open, and let the cheesecake cool inside for 1 hour.
Refrigerate for at least 4 hours, preferably overnight.

Step 4: Make the Cake Layer
Preheat your oven to 350°F (175°C).
Grease and flour a 9-inch round cake pan.
In a small bowl, whisk together flour, baking powder, and salt.
In another bowl, beat the eggs and sugar until thick and pale.
Gently fold in the flour mixture.
Heat the milk and butter together until melted, then stir into the batter along with the vanilla extract.
Pour the batter into the prepared pan and bake for 20-22 minutes, until golden and a toothpick inserted in the center comes out clean.
Cool completely.

Step 5: Assemble the Cheesecake
Carefully remove the chilled cheesecake from the springform pan.
Place the cooled cake layer gently on top of the cheesecake.

Step 6: Make the Chocolate Ganache
Heat heavy cream in a small saucepan until it begins to simmer.
Pour the hot cream over the chocolate chips in a bowl.
Let sit for 2 minutes, then stir until smooth and glossy.

Step 7: Top with Ganache
Pour the chocolate ganache over the top of the cake layer, letting it drip slightly over the edges.
Refrigerate for 30 minutes to set.

Step 8: Slice and Serve
Use a sharp knife dipped in hot water (and wiped dry) for clean slices.
Serve chilled or slightly softened at room temperature.