Step 1: Combine the crushed chocolate sandwich cookies and melted butter in a medium bowl. Stir until the crumbs are evenly moistened.
Step 2: Press the mixture firmly into the bottom of a 9-inch springform pan. Refrigerate for at least 15-20 minutes while preparing the filling.
Step 3: In a large bowl, beat the softened cream cheese with 1 cup granulated sugar and vanilla extract using an electric mixer on medium speed until smooth and creamy, about 2-3 minutes. Ensure there are no lumps.
Step 4: In a separate, chilled bowl, whip the cold heavy cream until stiff peaks form.
Step 5: Gently fold the whipped cream into the cream cheese mixture using a spatula until just combined. Be careful not to overmix.
Step 6: Pour the cheesecake filling over the chilled cookie crust in the springform pan. Smooth the top with an offset spatula. Refrigerate for at least 4-6 hours, or preferably overnight, to allow the cheesecake to set completely.
Step 7: In a medium saucepan, combine the mixed berries, ½ cup granulated sugar, and lemon juice. Cook over medium heat, stirring occasionally, until the berries break down and the mixture thickens, about 10-15 minutes. Mash some berries for a smoother sauce if desired.
Step 8: (Optional) For a perfectly smooth ‘blood’ sauce, press the berry mixture through a fine-mesh sieve to remove seeds and pulp. Let the sauce cool slightly.
Step 9: Once the cheesecake is fully set, carefully remove it from the springform pan. Pour the cooled berry topping over the cheesecake, allowing some to drip artfully down the sides for a ‘bloody’ effect. Refrigerate again for at least 30 minutes before serving.