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. Cook over medium heat until berries soften, about 5 minutes. Stir in cornstarch mixture 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. Blend in sour cream and vanilla.
05 - Divide filling in half. Fold melted dark chocolate into one half.
06 - Pour chocolate filling over crust, spreading evenly. Top with plain filling.
07 - Drop spoonfuls of strawberry puree on top. Use skewer or knife to swirl through batter creating marbled pattern.
08 - Place pan on baking sheet. Bake for 50-60 minutes until center is just set and slightly wobbly.
09 - Turn off oven, leave door slightly open, and let cheesecake cool for 1 hour inside.
10 - Refrigerate for at least 4 hours or overnight before serving.