Preheat your oven to 325°F (160°C).

In a mixing bowl, combine graham cracker crumbs, sugar, and melted butter until well mixed.

Press the crumb mixture into the bottom of a 9-inch springform pan.

Bake the crust in the preheated oven for 10 minutes.

In a large bowl, beat the softened cream cheese and sugar until smooth.

Add the eggs one at a time, mixing well after each addition.

Stir in the vanilla extract.

Blend in the sour cream until fully incorporated.

In a separate bowl, combine half of the cheesecake mixture with the melted chocolate.

Pour half of the plain cheesecake filling into the crust, followed by half of the chocolate mixture. Repeat and use a knife to swirl the mixtures together.

Bake the cheesecake for 60 minutes, or until the edges are firm but the center is slightly jiggly.

Turn off the oven and let the cheesecake cool slowly in the oven with the door ajar.

Chill the cheesecake in the refrigerator overnight before serving.