Combine the chocolate wafer crumbs and the butter, mixing well. Press the mixture into the bottom of a 9-inch springform pan; chill.
Beat the cream cheese on low speed with the electric mixer until light and fluffy; gradually add the sugar, mixing well. Add the eggs, one at a time, beating well after each addition. Stir in the sour cream, melted chocolate, cocoa and vanilla; mix well. Gently fold in the whipped cream; spoon into the prepared pan.
Bake at 300 degrees for 1 hour. Turn the oven off; allow the cheesecake to cool in the oven for an additional 30 minutes. Refrigerate overnight. Remove the sides of the springform pan and garnish with additional whipped cream, chocolate curls and maraschino cherries, if desired.