Grind graham crackers in a food processor until fine. Add butter and continue pulsing until the mixture is moistened. Press into bottom and up the sides about halfway of a 9-inch pie pan. Bake for 7 minutes. Cool completely before moving on to the next step.
To make the truffle filling:
Put chocolate in a medium-sized heat-proof bowl. In a small saucepan, bring the heavy cream just to a simmer. Pour over the chocolate. Let sit for about 1 minute then stir until smooth. Spread into the cooled crust. Freeze until firm, 20-30 minutes.
To make the whipped chocolate filling:
Heat chocolate, ½ cup of the cream, and vanilla in microwave for 20 second bursts, stirring between each one, until chocolate is melted and mixture is smooth. Be careful not to overheat! Let cool before proceeding.
Beat the remaining cup of cream on until thick. Add the chocolate mixture and continue to beat until soft peaks. Spread this over the truffle filing and refrigerate overnight.
To make the whipped cream:
Beat cream and powdered sugar together until stiff peaks form. Spread or dollop over pie as you wish. Use a grater or vegetable peeler to make chocolate shavings for garnish (optional). Store in refrigerator until serving.