Preheat oven to 350 degrees. Butter 8-inch springform pan and wrap the outer side of the pan with heavy duty aluminum foil. For crust, combine cookie crumbs with melted butter in small bowl and stir until crumbs are evenly moistened. Transfer to prepared springform pan. Press crumbs to evenly cover bottom of pan. Bake crust for 10 minutes. Cool on wire rack. To prepare cheesecake filling, beat cream cheese in a large bowl, using an electric mixer at medium speed, until light and fluffy. Add mascarpone and beat just until blended. Add sugar and beat until smooth. Add eggs, one at a time; then add the espresso and rum. When all of the ingredients are thoroughly blended, fold in chocolate using a rubber spatula. Pour mixture over the crust in prepared springform pan. Place pan in a larger baking pan and add enough boiling water to come halfway up the sides of the springform pan. Bake cheesecake in oven for 1 hour and 20 minutes or just until lightly golden and set. Turn off the oven and let cheesecake rest for 30 minutes with the door slightly ajar. Transfer cheesecake to a wire rack to cool completely. Remove aluminum foil, cover with plastic wrap, and refrigerate for 3 hours or overnight. To prepare topping, beat heavy cream with sugar and rum in medium bowl, using an electric mixer at high speed, until stiff. Spread whipped cream over the top of cheesecake, then sprinkle with chocolate. Remove sides of springform pan just before serving. Makes 12 servings