01 - Preheat oven to 325°F (160°C). Grease a 9-inch springform pan and line the bottom with parchment paper.
02 - Combine the crushed chocolate sandwich cookies with melted butter in a bowl until the mixture resembles wet sand. Press firmly and evenly into the bottom of the prepared pan. Bake for 10 minutes, then set aside to cool.
03 - In a large mixing bowl, beat the softened cream cheese and granulated sugar together using a hand or stand mixer until completely smooth and free of lumps. Add the peanut butter and blend until fully incorporated.
04 - Add the eggs one at a time, beating on low speed after each addition to avoid incorporating excess air. Mix in the vanilla extract and sour cream until just combined.
05 - Split the filling mixture evenly into two bowls. Fold the melted dark chocolate into one half, stirring until uniformly colored. Leave the other half as the plain peanut butter mixture.
06 - Pour the chocolate batter over the cooled crust and spread into an even layer. Spoon the peanut butter batter on top in dollops. Run a butter knife through the layers in gentle figure-eight motions to create a marbled effect.
07 - Bake for 50 to 60 minutes, until the edges are set and the center has a slight jiggle when gently shaken. Avoid overbaking, as the cheesecake will continue to set as it cools.
08 - Turn off the oven and crack the door open slightly. Let the cheesecake rest inside for 1 hour. This gradual cooling helps prevent surface cracks.
09 - Transfer the cheesecake to the refrigerator and chill for at least 4 hours, preferably overnight, before adding the topping.
10 - Heat the heavy cream in a small saucepan until steaming but not boiling. Remove from heat, add the chopped dark chocolate, and stir until smooth and glossy. Stir in the peanut butter until well blended. Let the mixture cool slightly until it reaches a spreadable consistency.
11 - Spread the topping evenly over the chilled cheesecake. Garnish with chopped roasted peanuts if desired. Slice into 12 portions with a sharp knife dipped in hot water for clean cuts. Serve chilled.