1. Place the chocolate and cream in the bowl fitted with the kneading/crushing blade. Launch the bowl at speed 3 at 110°F for 10 minutes. Add the powdered sugar and vanilla. Mix at speed 8 for 20 seconds.
2. Place the mixture in a separate bowl and cover with plastic wrap. Refrigerate for 1 hour 30 minutes to 2 hours.
3. Place the cocoa powder on a plate. Using a spoon, put a little chocolate mixture in your hands and form a 1-inch ball. Roll in cocoa. Repeat until all the mixture has been used.