Place the chopped chocolate in a microwave safe bowl and microwave on high heat for 1 minute. Stir well, then continue heating in 30 second increments, stirring between each, until it is completely melted. Set it aside to cool.
1 ½ cups (6 oz) bittersweet chocolate
In the bowl of a stand mixer fitted with a whisk attachment, whip the heavy cream, powdered sugar, and vanilla on medium high speed until stiff peaks form (the peaks should hold their shape when you pull the whisk out). Carefully scoop the whipped cream into a large bowl then set aside in the fridge.
1 ¼ cup heavy whipping cream, ⅓ cup powdered sugar, 1 tablespoon vanilla
In the now empty bowl, use the paddle attachment to beat the cream cheese and granulated sugar on medium speed until really smooth, about 30-60 seconds. Use a rubber spatula to scrape the bowl well. Add the sour cream and beat again on medium-high speed for 2-3 minutes. The mixture should be fluffy, but still relatively thick.
24 oz (3 bricks) cream cheese, ⅔ cup granulated sugar, ¼ cup sour cream
Pour the cooled chocolate into the cream cheese mixture. Mix on low speed until it is fully combined. You'll want to pause and scrape the sides and bottom of the bowl several times to help it mix evenly. It should be smooth and even in color.
Using a rubber spatula, fold in the whipped cream you made earlier. Work gently, turning the bowl after each fold, to help it distribute evenly without deflating. Keep going until the mixture is evenly combined, with no white streaks remaining. Stop as soon as it is combined, being careful not to overmix.
Pour the filling into the prepared crust, then use an offset spatula to smooth the top. Once totally smooth, cover it with plastic wrap and place in the refrigerator for at least 12 hours or overnight.
Once chilled, remove the cheesecake from the fridge and carefully release it from the pan. If it appears to be sticking, carefully run a sharp knife around the edge before releasing it. Serve with fresh whipped cream and chocolate shavings, if desired.
Whipped cream, Chocolate shavings