01 - Preheat oven to 325°F (160°C). Grease a 9-inch (23 cm) springform pan and line the bottom with parchment paper.
02 - Combine the crushed chocolate sandwich cookies with the 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 smooth peanut butter and blend until fully incorporated.
04 - Add the eggs one at a time, beating on low speed after each addition just until combined. Mix in the vanilla extract and sour cream, being careful not to overbeat.
05 - Divide the filling mixture evenly into two portions. Stir the melted dark chocolate into one half, mixing until uniform in color. Leave the other half as the plain peanut butter mixture.
06 - Pour the chocolate filling over the cooled crust and spread into an even layer. Spoon the peanut butter filling gently on top. Run a butter knife through the layers in a figure-eight motion to create a marbled effect.
07 - Bake on the center rack for 50 to 60 minutes, until the edges are firmly set but the center still has a slight jiggle when gently shaken.
08 - Turn off the oven and crack the door open. Let the cheesecake rest inside the cooling oven for 1 hour to prevent cracking from sudden temperature changes.
09 - Transfer the cheesecake to the refrigerator and chill for at least 4 hours, preferably overnight, until fully set.
10 - In a small saucepan, heat the heavy cream until just steaming (do not boil). Remove from heat, add the chopped dark chocolate, and stir until silky smooth. Stir in the creamy peanut butter until well blended. Let the ganache cool slightly, then spread it evenly over the chilled cheesecake.
11 - Sprinkle chopped roasted peanuts over the top if desired. Slice with a sharp knife dipped in hot water for clean portions, wiping the blade between cuts. Serve chilled.