Mix cornstarch and water in a small bowl until smooth. Set aside.
Combine the heavy cream and chocolate chips in a small saucepan or microwave-safe bowl or large cup. Heat, stirring frequently, until the chips melt and the mixture is smooth. Remove from the heat, stir in the espresso powder, and set the mixture aside.
Place the cream cheese in the bowl of an electric mixer, beat on low speed for 2-3 minutes until smooth and free of any lumps. Add sugar and cocoa powder; continue mixing until incorporated. Gradually add sweetened condensed milk and beat until creamy, for 1-2 minutes. Add vanilla extract and cornstarch mixture; beat until well incorporated.
Add melted chocolate mixture; beat until well incorporated.
Pour the mixture over the crust; tap gently to remove any air bubbles.
Place the cheesecake pan on MULTIPLE LAYERS of heavy-duty aluminum foil and fold up the sides around it (this is to keep the water from seeping into the cheesecake). Place the cake pan in a large roasting pan. Pour hot water into the roasting pan until the water is about halfway up the sides of the cheesecake pan.
Bake for 40 minutes or until the edges are just barely puffed. The center of the cheesecake should still wobble when you remove it from the oven. Turn the oven off and allow to cool for 40 minutes in the oven with the door closed. Remove the cake from the oven and set it on a rack to finish cooling. After 15 minutes on a wire rack, carefully run a knife between the cheesecake and the inside of the pan. Don’t remove the sides of the pan yet.
When it's completely cool, cover the cake, and refrigerate it until ready to serve.
Loosen the cheesecake from the sides of the pan by running a thin metal spatula around the inside rim. Unmold and transfer to a cake plate.