Add the cream cheese to a large bowl. Use an electric mixer to cream the cream cheese. Gradually add in 1 cup of the powdered sugar, cocoa powder and the vanilla; set aside.
In a separate large bowl, use an electric mixer to start whipping the cream. Once it begins to thicken slightly, sprinkle in the ¼ cup powdered sugar. Continue to mix until stiff peaks form (peaks should stand upright when you run the beaters through the cream).
Use a rubber spatula to fold in HALF of the whipped cream into the cream cheese mixture. Fold gently, scraping the sides and the bottom of the bowl, until both mixtures are completely combined. Then fold in the rest of the whipped cream. Transfer the chocolate mousse to serving dishes. Sprinkle chocolate shavings on top, if desired. Refrigerate for at least a couple of hours before serving.