Beat cream cheese and sugar until fluffy. Add in egg, vanilla, and flour and beat until well combined. Add in chocolate and beat until well combined. Set aside.
Chocolate Bundt Cake:
Preheat oven to 350F. Grease a 10 or 12 cup Bundt pan and dust with cocoa powder.
In a medium bowl, combine cocoas, espresso powder, chopped chocolate and boiling water. Cover and let sit 5 minutes. Whisk until smooth. Let cool to room temperature and whisk in buttermilk. Set aside.
In a medium bowl, whisk flour, salt, and baking soda. Set aside.
Place butter in the bowl of a stand mixer fitted with the paddle attachment. Beat on med-high until pale. Add in sugar and beat until well combined (approx. 3 mins).
Reduce speed and add in eggs one at a time, fully incorporating after each addition. Add in vanilla.
Alternate adding flour mixture and chocolate mixture, beginning and ending with the flour (3 additions of flour, 2 additions of chocolate). Mix just until combined.
Dollop some cake batter into the Bundt pan and nudge into the cracks with a spatula. Add in more cake batter until pan is almost half full.
Carefully dollop in cheesecake filling being sure not to let it touch the sides.
Top with remaining cake batter and smooth with a spatula.**
Whack cake pan on the counter to get rid of any bubbles and fill in any cracks. Bake for 50-60mins or until a cake tester comes out mostly clean. Rotate pan after 40mins.
Cool in Bundt pan for 10mins. Whack Bundt pan on the counter to loosen cake and turn out onto cooling rack to cool completely.
* If you don't have black cocoa, just use Dutch-processed. ** Be sure to only fill pan no more than 3/4 full. If you have batter leftover, you can bake it alongside the Bundt in a loaf pan or in cupcake tins.