In a medium bowl, combine graham cracker crumbs, sugar and melted butter. Toss to coat all. Transfer to a deep 9-inch pie plate or spring form pan. Press into the bottom and sides with the back of a fork or spoon.
Bake for 5-7 minutes, or until it starts to brown. Remove and set aside. Keep oven on.
Using a a stand mixer with paddle attachment or electric hand mixer in a large mixing bowl, cream together cream cheeses. Add sour cream and continue to beat until smooth.
In a small mixing bowl, beat together sugar, flour, vanilla and eggs.
Add sugar mixture to cream cheese mixture in 2-3 increments, blending fully between each addition.
Pour 1/3 of cheesecake into into the pie crust. Reserve an additional 1/3, set aside.
Heat chocolate in microwave bowl in 30 second increments, stirring in between, until creamy. Blend into remaining 1/3 cheesecake batter to make the chocolate swirl.
Add large dollops of chocolate cheesecake on top of the vanilla cheesecake. Add additional dollops of remaining vanilla cheesecake batter on top of chocolate until pie crust is full.
Using a toothpick, make small and large swirls to create the marbleized effect. Over swirling will just mix them into a milky, light chocolate, so take it easy.
Create a water bath by finding a cooking vessel you can set the cheesecake in. Fill it with enough water to cover the bottom. Set cheesecake in water bath, being careful to not overflow the water into your cheesecake.
Carefully place oven and bake for 40 minutes. If the edges of the crust or top starts to brown too much, lightly place a leaf of aluminum foil over the top of the cheesecake.
Remove from the oven and allow to cool for 20-30 minutes. Cover and refrigerate for 3-4 hours before serving.
Garnish with chocolate sauce, whipped cream or maraschino cherries.
If you've tried this recipe, come back and let us know how it was!