Preheat oven to 325°F (160°C).

Prepare the crust: In a medium bowl, combine graham cracker crumbs, melted butter, and sugar. Press the mixture firmly into the bottom of a 9-inch springform pan. Bake for 10 minutes, then set aside to cool.

Make the cheesecake filling: In a large mixing bowl, beat the softened cream cheese and sugar together until smooth and creamy. Add the melted dark chocolate, eggs, and vanilla extract, and beat until fully combined.

Assemble the cheesecake: Pour the cheesecake mixture over the prepared crust in the springform pan. Smooth the top with a spatula.

Bake: Place the cheesecake in the preheated oven and bake for 45-55 minutes, or until the center is set but still slightly jiggly.

Cool and chill: Remove the cheesecake from the oven and let it cool in the pan for 10 minutes. Then refrigerate for at least 4 hours, preferably overnight, to allow the flavors to set.

Prepare raspberry topping: In a small saucepan, heat the fresh raspberries and sugar over low heat, stirring occasionally, until the raspberries break down and create a sauce. Remove from heat and let it cool.

Serve: When ready to serve, remove the cheesecake from the springform pan and top with the raspberry sauce. Optionally, garnish with fresh raspberries and a dusting of cocoa powder.