01 - Preheat oven to 350°F. Grease a 9-inch springform pan and line bottom with parchment paper.
02 - Combine crushed chocolate biscuits, melted butter, and sugar in a bowl. Press evenly into pan bottom. Bake for 10 minutes, then cool.
03 - Combine strawberries, sugar, and lemon juice in saucepan over medium heat until berries soften, about 5 minutes. Stir in cornstarch slurry and cook until thickened, 1-2 minutes. Puree until smooth and cool completely.
04 - Beat cream cheese and sugar until smooth. Add eggs one at a time, mixing well after each addition. Blend in sour cream and vanilla extract.
05 - Divide filling in half. Fold melted dark chocolate into one portion until fully incorporated.
06 - Pour chocolate filling over crust, spreading evenly into a smooth layer.
07 - Top with remaining plain cheesecake filling, spreading carefully to create an even second layer.
08 - Drop spoonfuls of strawberry puree across the surface. Use a skewer or knife to gently swirl through batter, creating a marbled pattern.
09 - Place pan on baking sheet. Bake for 50-60 minutes until center is just set and slightly wobbly.
10 - Turn off oven and crack door open slightly. Let cheesecake cool inside for 1 hour to prevent cracking.
11 - Refrigerate for at least 4 hours or overnight until fully set before releasing from pan and serving.