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 bowls. Fold the melted dark chocolate into one half, stirring gently until uniform in color. 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 or offset spatula through both 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—the residual heat will continue to set the center.
08 - Turn off the oven, crack the door open slightly, and let the cheesecake cool inside for 1 hour. This gradual cooling helps prevent cracks from forming on the surface.
09 - Transfer the cheesecake to the refrigerator and chill for at least 4 hours, preferably overnight, until fully set and firm.
10 - Heat the heavy cream in a small saucepan over medium heat until it begins to steam (do not boil). Remove from heat, add the chopped dark chocolate, and let sit for 2 minutes. Stir until smooth and glossy, then blend in the creamy peanut butter. Cool the ganache slightly until it thickens to a spreadable consistency, then pour over the chilled cheesecake and spread evenly.
11 - Sprinkle chopped roasted peanuts over the topping if desired. Slice with a warm, clean knife for neat portions and serve chilled.