Prepare the pan: Preheat oven to 350°F. Wrap the outside of a 9-inch springform pan tightly with aluminum foil to prevent water from seeping in during the water bath.
Make the crust: Pulse Oreo cookies in a food processor until fine crumbs form. Mix with melted butter until mixture resembles wet sand. Press firmly into the bottom of prepared pan. Bake for 10 minutes, then set aside to cool.
Melt chocolate: Melt 8 ounces chopped dark chocolate using a double boiler or microwave in 30-second intervals, stirring between each burst. Set aside to cool slightly.
Make filling: Beat cream cheese in food processor or with electric mixer until completely smooth. Add sugar, cocoa powder, espresso powder, and vanilla. Beat until combined.
Add eggs: Add eggs one at a time, beating just until incorporated after each. Do not overmix. Fold in heavy cream with a rubber spatula, then slowly pour in the cooled melted chocolate, stirring until evenly colored and thick.
Assemble: Pour half of filling over cooled crust. Scatter 1 cup fresh raspberries evenly in a single layer. Pour remaining filling over raspberries, making sure all berries are covered. Tap pan gently to release air bubbles.
Water bath: Place springform pan in a large roasting pan. Put in preheated oven, then carefully pour hot water into roasting pan until it comes 1 inch up the sides of the springform pan.
Bake: Bake for 1 hour and 10 minutes, until center is set but still slightly jiggly. Remove from water bath and carefully loosen foil. Immediately run a knife around the edge of pan to prevent cracking.
Cool and chill: Cool completely in pan on wire rack. Transfer to refrigerator and chill for at least 6 hours or overnight.
Make ganache: Place 6 ounces chopped chocolate in a bowl. Heat 1/2 cup heavy cream until boiling, pour over chocolate, let sit 1 minute. Whisk until smooth and glossy. Add butter and stir until melted. Cool to room temperature.
Finish: Remove chilled cheesecake from springform pan. Pour ganache over top, allowing it to drip down sides. Garnish with remaining fresh raspberries. Slice with a hot, clean knife.