Step 1: Prepare the Crust

1. Preheat your oven to 350°F (175°C).
2. Combine the graham cracker crumbs, melted butter, and sugar in a bowl.
3. Press the mixture firmly into the bottom of a springform pan.
4. Bake for 10 minutes and let it cool.

Step 2: Make the Cheesecake Filling

1. Blend the softened cream cheese and sugar until smooth.
2. Add eggs one at a time, mixing after each addition.
3. Stir in the vanilla extract and sour cream.
4. Pour over the cooled crust and bake at 325°F (160°C) for about 50 minutes.

Step 3: Prepare the Custard Filling

1. Heat milk, sugar, and cornstarch in a saucepan until thickened.
2. Whisk the egg yolks and temper them with the hot milk mixture.
3. Return the mixture to the saucepan and cook for 2-3 minutes.
4. Remove from heat and stir in the vanilla extract. Cool completely.

Step 4: Assemble the Layers

1. Spread the cooled custard over the baked cheesecake.
2. Refrigerate for at least 2 hours to set.

Step 5: Make the Ganache

1. Heat the heavy cream until it begins to simmer.
2. Remove from heat and stir in chocolate chips until smooth.
3. Cool slightly before pouring over the custard layer.

Step 6: Chill and Serve

1. Refrigerate the assembled cheesecake for at least 4 hours or overnight.
2. Remove from the springform pan, slice, and serve chilled.