Grease a springform pan and line the bottom with parchment paper.

Chop the chocolate into small pieces. Place in the top pan of a double boiler over simmering water, stirring until the chocolate is fully melted and smooth. Set aside to cool to room temperature. Be sure no moisture or water gets into the melted chocolate.

Combine chocolate graham cracker crumbs and granulated sugar in a mixing bowl or directly in the bottom of a springform pan. Stir to combine evenly.

Pour the melted butter into the graham cracker crumb mixture and stir to make a sandy mixture. Press the crust across the bottom and up the sides of the springform pan. Place crust in the refrigerator to firm up while preparing the cheesecake.

In a large mixing bowl, beat together cream cheese and sour cream until fluffy and smooth.

Add the powdered sugar, beating until combined. Beat in the vanilla extract.

When the chocolate is at room temperature, pour it into the cream cheese mixture and beat to combine.

Add the heavy cream to the cheesecake mixture, beating for 1-2 minutes longer until fluffy and well combined. Cheesecake mixture should form soft peaks.

Spread the cheesecake filling evenly into the chilled crust. Use an offset spatula to smooth the top of the cheesecake.

Place cheesecake in the refrigerator for at least 4 hours.

Garnish with fresh raspberries or whipped cream. You can also drizzle with chocolate ganache.