Preheat the oven to 325°F. Prepare a 9x13-inch pan by lining the bottom and sides with parchment paper. Spray lightly with non-stick spray.

Add flour, sugar, cocoa powder, and salt to a food processor. Cube 9 Tablespoons (126g) of butter and place on top of the dry ingredients in the food processor. Pulse until fine crumbles. Melt 5 Tablespoons (70g) of butter and drizzle over the crumbles. Pulse 5-6 times until the mixture balls together. Press the mixture evenly into the bottom of the 9x13-inch pan. Set aside. Do not bake.

Add the chocolate and the cream to a microwave-ready bowl. Microwave for 30 seconds and stir the mixture. Microwave in 15-second intervals, stirring after each interval, until the chocolate mixture is smooth and the chocolate has melted. Set aside to cool.

In a large mixing bowl, add the bricks of cream cheese, sugar, cocoa powder, and vanilla. With a mixer on low speed, combine the ingredients. Add the cooled chocolate mixture and continue to mix on low speed until no white remains. Mix in eggs, one at a time. Then, add sour cream and mix just until combined. Fold mixture with a spatula until smooth.

Pour cheesecake mixture onto the chocolate shortbread crust. Smooth the top. Bake at 325°F for 38-39 minutes, until cheesecake has lost its shine, the edges bounce back when lightly touched, and the center is jelly-like, not liquidy. Remove the cheesecake from the oven and let it cool at room temperature. Chill in the refrigerator for at least 1 hour before adding the ganache topping.

Prepare the ganache topping by placing the chocolate and cream in a microwave-safe bowl. Microwave for 30 seconds and stir. Continue microwaving and stirring in 15-second intervals until the mixture is smooth and the chocolate has melted. Let cool slightly. Remove the chilled cheesecake from the 9x13-inch pan, using the parchment paper. While keeping the cheesecake on the parchment and a heavy board to support it, pour the cooled ganache over the top. Spread evenly and smooth the top. Chill in the refrigerator until the ganache hardens. Cut the chilled cheesecake into cubes. Top with optional garnishes, if desired.