In a large bowl with an electric hand mixer, beat the cream cheese and granulated sugar until smooth. Add the sour cream and vanilla. Beat again. Add the whipped topping and mix until combined.
Pour half of the cheesecake filling into the bottom of a prepared chocolate crust. Add cocoa powder and powdered sugar to the remaining cheesecake filling. Beat with hand mixer until combined. Spread evenly over the vanilla cheesecake layer.
In the bowl of a stand mixer fitted with the whisk attachment, beat the heavy cream and powdered sugar until stiff peaks. Spread or pipe whipped cream onto the top of the chocolate cheesecake layer. Use a vegetable peeler to cut chocolate shavings from a candy bar over the top of the whipped cream layer. REFRIGERATE 4-6 hours or overnight to set completely.