Preheat your oven to 325°F (160°C). Grease a 9-inch (23cm) springform pan with butter or non-stick spray.

In a medium-sized bowl, combine the chocolate graham cracker crumbs, granulated sugar, and melted butter for the crust. Mix until the crumbs are evenly coated with butter.

Press the crumb mixture into the bottom of the prepared springform pan, using the back of a spoon or your fingertips to pack it tightly and create an even layer. Set aside.

In a large mixing bowl, beat the cream cheese and granulated sugar together until smooth and creamy, about 2-3 minutes on medium speed.

Add the eggs one at a time, mixing well after each addition. Scrape down the sides of the bowl as needed.

Mix in the vanilla extract until well combined, then gently fold in the sour cream until just incorporated.

Pour the cheesecake filling over the prepared crust in the springform pan, spreading it out evenly with a spatula.

Bake the cheesecake in the preheated oven for 50-55 minutes, or until the edges are set and the center is slightly jiggly.

Remove the cheesecake from the oven and let it cool completely on a wire rack. Once cooled, refrigerate it for at least 4 hours or overnight to chill.

To make the chocolate mousse, heat the heavy cream in a small saucepan over medium heat until it just begins to simmer. Remove from heat and add the chocolate chips to the cream.

Let the chocolate sit in the hot cream for 1-2 minutes, then stir until smooth and well combined. Set aside to cool to room temperature.

In a separate mixing bowl, whip the remaining heavy cream until it forms stiff peaks. Gently fold the whipped cream into the cooled chocolate mixture until no streaks remain.

Spread the chocolate mousse evenly over the chilled cheesecake in the springform pan. Return the cheesecake to the refrigerator and let it chill for an additional 2 hours.

Just before serving, prepare the whipped cream topping. In a mixing bowl, whip together the heavy cream, powdered sugar, and vanilla extract until stiff peaks form.

Pipe or spread the whipped cream over the top of the chocolate mousse layer. If desired, garnish with chocolate shavings or a dusting of cocoa powder.

Carefully remove the sides of the springform pan before slicing and serving the chocolate mousse cheesecake. Enjoy!