Preheat the oven to 325°F (160°C). Lightly grease a 9-inch springform pan.

For the crust, combine chocolate cookie crumbs and melted butter in a bowl. Press the mixture into the bottom of the pan to form a crust. Set aside.

For the raspberry swirl, place raspberries, sugar, and lemon juice in a saucepan over medium heat. Cook for 5-7 minutes until raspberries break down.

Stir in the cornstarch mixture and cook for another 2 minutes until thickened. Remove from heat and strain through a fine sieve to remove seeds. Let cool.

For the cheesecake filling, beat the softened cream cheese in a large bowl until smooth. Add sugar and mix until creamy.

Add melted dark chocolate, sour cream, eggs, and vanilla extract. Beat until smooth.

Pour half the cheesecake batter over the crust. Spoon half of the raspberry sauce over the batter and gently swirl with a knife. Repeat with remaining batter and raspberry sauce.

Bake for 50–60 minutes, until the center is just set. Turn off the oven and crack the door open. Let cool in the oven for 1 hour.

Chill the cheesecake in the refrigerator for at least 4 hours or overnight before slicing.