In a medium microwave save bowl, mix together the chocolate chips and 3/4 cup of whipping cream. Microwave in 30 second intervals, stirring after each interval until smooth. Stir in the powdered sugar and vanilla. Set aside.
Meanwhile, whip the rest of the cream until stiff peaks form. Add in the chocolate mixture, and mix until fully incorporated.
Refrigerate (or put in the freezer) overnight, or at least 8 hours, before serving.