Preheat your oven to 350°F (175°C). In a mixing bowl, combine graham cracker crumbs, melted unsalted butter, and granulated sugar until evenly moistened. Press this mixture firmly into the bottom of a springform pan, ensuring an even layer. Bake for 8-10 minutes, until lightly golden. Allow the crust to cool while you prepare the cheesecake filling.

In a large bowl, beat softened cream cheese and granulated sugar together until smooth and creamy. Add sour cream and vanilla extract, mixing until fully blended. This should take about 3-4 minutes on medium speed. Once your mixture is velvety, pour it over the cooled crust, smoothing it with a spatula for an even surface.

Place the springform pan in the oven and bake at 350°F (175°C) for 25-30 minutes. The cheesecake should be set around the edges but slightly jiggly in the center. This ensures a creamy texture. Once done, turn off the oven, crack the door open slightly, and let the cheesecake cool for another 30 minutes.

While the cheesecake cools, rinse fresh raspberries under cold water and gently pat them dry. In a bowl, sprinkle them with powdered sugar and let them macerate for about 10-15 minutes. Layer the sweetened raspberries evenly over the slightly cooled cheesecake.

In a saucepan, heat heavy cream over medium heat until it just begins to simmer. Remove from heat and pour over chopped dark chocolate in a bowl. Stir gently for about 2-3 minutes until the chocolate is fully melted and the mixture is glossy.

Carefully pour the warm ganache over the topped cheesecake, spreading it evenly with a spatula to cover all the raspberries. Allow the cheesecake to cool at room temperature for about 15 minutes before refrigerating it for at least 4 hours, preferably overnight.

When ready to serve, gently run a knife around the edges of the springform pan before releasing it. Slice the cheesecake into wedges and present it on a beautiful platter. Garnish with extra fresh raspberries or chocolate shavings if desired.