Place the chopped chocolate in a microwave safe container and microwave for 30 second intervals, stirring after each one until the chocolate is completely melted. Set aside to let it cool.
Whip the heavy cream in a medium bowl until stiff peaks form. Set aside.
In a stand mixer or using a hand mixer, beat together the softened cream cheese and the granulated sugar until creamy and combined.
Add the cocoa powder and sour cream and mix until smooth.
Mix in the melted chocolate until combined.
Fold the whipped cream into the cream cheese mixture gently until no white streaks remain.
Pour the cheesecake filling into the crust and smooth the top with a spatula.
Cover the cheesecake with foil or plastic wrap and refrigerate for 12 hours or overnight. Top with the peanut butter mousse before serving.