1. Preheat oven to 325°F (163°C). Grease a 9-inch springform pan and line the bottom with parchment paper.

2. In a bowl, mix crushed cookies, melted butter, and sugar until combined. Press firmly into the bottom of the prepared pan. Bake for 10 minutes, then cool slightly.

3. In a small saucepan, combine raspberries, sugar, and lemon juice over medium heat. Cook for 5–6 minutes, mashing berries until juicy. Stir in cornstarch slurry and cook 1–2 minutes until thickened. Strain to remove seeds, then cool.

4. Melt dark chocolate in a heatproof bowl over simmering water (or microwave in 20-second bursts) until smooth. Cool slightly.

5. In a large bowl, beat cream cheese and sugar until smooth and fluffy. Add cocoa powder, vanilla, and salt; mix well.

6. Beat in eggs one at a time, scraping sides as needed.

7. Mix in sour cream, then slowly add melted chocolate and beat until combined.

8. Pour half the cheesecake batter into the crust, spoon half the raspberry sauce on top, and swirl gently with a knife.

9. Repeat with remaining batter and raspberry sauce, swirling again for a marbled effect.

10. Bake for 55–65 minutes, or until the center is just set and slightly jiggly.

11. Turn off oven, crack the door open, and let cheesecake cool for 1 hour in the oven to prevent cracking.

12. Chill at least 6 hours or overnight before serving.

13. Top with fresh raspberries, chocolate shavings, or ganache before serving.