Preheat the oven to 160°C (320°F).

Mix crushed chocolate cookies with melted butter until combined. Press the mixture into the bottom of a springform pan. Bake for 10 minutes, then set aside to cool.

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

Pour the cheesecake filling over the cooled crust. Bake in the preheated oven for 50-60 minutes, or until the center is set. Let it cool at room temperature, then refrigerate for at least 4 hours or overnight.

In a saucepan, combine mixed berries, sugar, and lemon juice. Cook over medium heat until the mixture thickens. Let it cool, then spread over the chilled cheesecake.

Melt dark chocolate and butter in a microwave or double boiler. Drizzle over the berry topping.