Preheat oven to 350°F (175°C). In a food processor, pulse Oreo cookies into a fine crumb. Mix with melted butter. Press firmly into the bottom of a 9-inch springform pan. Bake for 10 minutes. Let cool.

In a saucepan, combine raspberries, sugar, and lemon juice over medium heat. Simmer until berries break down. Whisk in the cornstarch slurry (1 tsp cornstarch + 1 tbsp water) and simmer for 2 more minutes until thickened. Strain to remove seeds and cool completely.

Melt the chopped dark chocolate in a double boiler or microwave until smooth. Let cool slightly.

In a large bowl, beat room temperature cream cheese until completely smooth. Add sugar and beat until combined. On low speed, mix in eggs one at a time. Mix in sour cream, vanilla, espresso powder, and the melted chocolate until just combined.

Pour half the cheesecake filling over the crust. Dollop with half the raspberry sauce. Add the remaining filling, then dollop the remaining sauce. Gently swirl with a knife.

Wrap the pan in two layers of heavy-duty foil. Place in a large roasting pan. Add boiling water to the roasting pan until it comes halfway up the sides of the springform pan.

Bake for 65-75 minutes, until the edges are set and the center has a slight wobble.

Turn off the oven and crack the door. Let the cheesecake cool in the oven for 1 hour. Remove from the water bath and cool completely on a wire rack. Chill in the refrigerator for at least 6 hours or overnight.

To make the ganache, place chocolate chips in a heatproof bowl. Heat heavy cream until simmering, then pour over the chocolate. Let sit for 5 minutes, then whisk until smooth. Pour over the chilled cheesecake. Refrigerate for 30 minutes to set.