1. In a large glass measuring cup, add 3/4 cup heavy cream, sugar-free chocolate, and espresso powder (if using).  Microwave on high for 1 minute.  Stir until all the chocolate has melted.  If the chocolate has not melted, return the bowl to the microwave for an additional 15 seconds.  Add the vanilla and powdered sweetener and stir to combine.  Let the mixture sit for 5 minutes, stirring every so often, or until it cools slightly.
2. While the chocolate mixture is cooling, add the remaining 3/4 cup of heavy cream to a mixing bowl and beat on high for 2-3 minutes or until stiff peaks form.
3. Add cooled chocolate mixture, one-third at a time, beating after each addition until well mixed.
4. Spoon the filling into the cold crust (if using).  Chill pie for at least 8 hours or up to 2 days.  Serve with optional topping if desired.

Optional Topping:

1. On the day of serving the pie, whip together 1 cup cold heavy cream with 1/4 cup powdered sweetener until stiff peaks form.  Spread over cake and sprinkle with chocolate shavings.