Preheat your oven to 350°F (175°C). In a mixing bowl, combine chocolate cookie crumbs, melted unsalted butter, and granulated sugar until fully blended. Press this mixture firmly into the bottom of a springform pan to form a crust. Bake for 10 minutes, then let it cool while preparing the cheesecake filling.

In a large mixing bowl, beat the cream cheese until smooth and creamy. Gradually add the granulated sugar, blending until combined. Add the eggs one at a time, mixing well after each addition. Stir in vanilla extract, sour cream, and melted chocolate.

In a separate bowl, blend fresh strawberry puree with sugar and lemon juice until smooth. Set aside as you assemble your cheesecake layers.

Pour the chocolate cheesecake filling over the cooled crust. Using a spoon, drop dollops of strawberry puree onto the filling. Gently swirl the puree into the chocolate filling to create a marbled design.

Bake for 50 to 60 minutes. The edges should set while the center remains slightly jiggly. Turn off the oven and leave the cheesecake inside for an hour to cool gradually.

Remove the cheesecake from the oven and let it cool to room temperature. Cover and place in the refrigerator for at least 4 hours, or overnight.

To serve, gently release the cheesecake from the springform pan. Slice with a warmed knife for clean cuts and serve each slice chilled.