Preheat the oven to 325°F. Line the bottom of a 9-by-13-inch baking pan with parchment paper.

To make the crust, in a bowl, stir together the graham cracker crumbs and sugar until blended. Add the melted butter and stir until well incorporated.

Add the graham cracker crumb mixture to the prepared pan. Pat down evenly on the bottom of the pan until it is completely covered with the crumbs. Bake for 5 minutes, then transfer the pan to a wire rack and let cool.

Reduce the oven temperature to 225°F. 

To make the cheesecake, in a bowl, using an electric mixer, beat together the cream cheese and sugar until well blended, then beat in the vanilla. Add the eggs one at a time, beating until incorporated before add the next one. Then beat for about 5 minutes.

Meanwhile, in a small bowl, stir together the cocoa powder and water to form a paste. Add the cocoa mixture to the cheesecake mixture and beat until well blended.

Pour the filling into the graham cracker crust and, using the back of a spoon, smooth the filling evenly in the pan.

Bake at 225°F for 1 hour and 15 minutes to 1 hour and 25 minutes. The cheesecake is done when it looks and feels dry when you place your hand on top of it and it does not jiggle.

Let the cheesecake cool to room temperature, then freeze overnight. Do not defrost when ready to serve.

To make the ganache, put the chocolate chips in a bowl. In a microwavable bowl, combine the cream and butter and microwave until the mixture comes to a simmer. Pour the cream mixture over the chocolate chips. Do not stir, but jiggle the bowl until the chips are covered with the cream mixture. Let stand for 5 minutes. Using a whisk and starting in the center of the bowl, very slowly start to mix the chocolate chips into the cream mixture. Continue to mix very slowly and you will see the dark color of the ganache start to form. Continue to mix until the cream and butter are well blended into the ganache. Let cool until slightly firm. Transfer the ganache to a pastry bag.

When ready to serve, cut the frozen cheesecake into 24 equal pieces. Using the pastry bag, pipe a ring of ganache on top of each piece. Add a small spoonful of raspberry preserves in the center and top each with a fresh raspberry.