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, mixing until the crumbs are evenly moistened. Press the mixture firmly and evenly into the bottom of the prepared springform pan to form a compact crust layer.
03 - Bake the crust for 10 minutes. Remove from the oven and set aside to cool completely while preparing the filling.
04 - In a large mixing bowl, beat the softened cream cheese and granulated sugar together using a hand or stand mixer on medium speed until completely smooth and free of lumps. Add the smooth peanut butter and blend until fully incorporated.
05 - Add the eggs one at a time, beating on low speed after each addition just until combined. Stir in the vanilla extract and sour cream, mixing gently until the batter is uniform. Avoid overmixing to prevent excess air in the batter.
06 - Divide the filling mixture evenly into two separate bowls. Into one half, fold the melted and slightly cooled dark chocolate until uniformly blended. Leave the other half as the plain peanut butter mixture.
07 - Pour the chocolate filling over the cooled crust and spread into an even layer. Gently spoon the peanut butter filling on top in dollops. Using a butter knife or offset spatula, lightly swirl through both layers in a figure-eight motion to create a marbled effect.
08 - Bake on the center rack for 50 to 60 minutes. The cheesecake is done when the edges are fully set and the center has a slight jiggle when gently shaken. Avoid opening the oven door during baking.
09 - Turn off the oven and crack the door open slightly. Allow the cheesecake to rest inside the cooling oven for 1 hour. This gradual cooling helps prevent cracks from forming on the surface.
10 - Transfer the cheesecake to the refrigerator and chill for at least 4 hours, preferably overnight, until completely set and firm throughout.
11 - In a small saucepan, heat the heavy cream over medium-low heat until steaming and just beginning to simmer. Remove from heat, add the chopped dark chocolate, and let stand for 1 minute. Stir until the ganache is smooth and glossy, then blend in the creamy peanut butter. Allow the topping to cool slightly until it reaches a spreadable consistency.
12 - Spread the topping evenly over the chilled cheesecake. Garnish with chopped roasted peanuts if desired. Slice with a sharp knife dipped in hot water for clean portions and serve.