Preheat your oven to 325°F (163°C). Grease a 9-inch springform pan and wrap it in aluminum foil, ensuring no water seeps in during baking. In a medium bowl, mix together chocolate wafer crumbs and melted butter until well combined. Press this mixture firmly into the bottom of the pan to form an even layer. Bake for 10 minutes, then remove from the oven and set aside to cool.

Using a double boiler, melt the bittersweet chocolate, stirring until smooth, then allow it to cool slightly. In a food processor, combine room-temperature cream cheese, granulated sugar, light brown sugar, and unsweetened cocoa powder. Blend until smooth, then add the beaten eggs, egg yolks, and heavy cream, mixing until just combined. Fold in the melted chocolate and vanilla extract for an irresistibly rich filling.

Pour the cheesecake filling over the cooled crust, spreading it evenly. Prepare a water bath by placing the filled springform pan into a larger roasting pan; fill the roasting pan with hot water until it reaches halfway up the sides of the springform. Bake in the preheated oven for 1 hour and 10 minutes, until the edges are set but the center is slightly jiggly. Once done, cool the cheesecake in the pan on a wire rack for about an hour before refrigerating it for at least 6 hours.

In a small saucepan, heat the heavy cream over medium heat until just simmering. Remove from heat and pour over the chopped semi-sweet chocolate in a mixing bowl. Whisk the mixture until smooth and glossy, ensuring all chocolate is melted. Stir in room-temperature butter until fully combined, creating a luxurious ganache that will top your Ultimate Chocolate Cheesecake.

After the cheesecake has chilled for at least 6 hours, remove it from the refrigerator. Pour the prepared ganache evenly over the chilled cheesecake, using a spatula to ensure a smooth layer. Allow the ganache to set at room temperature for about 1 hour before carefully releasing the sides of the springform pan. Slice and serve your decadent Ultimate Chocolate Cheesecake, and enjoy a true delight!