01 - Preheat oven to 325°F. Grease a 9-inch springform pan and line the bottom with parchment paper. Wrap the outside of the pan tightly with aluminum foil to prevent water bath leakage if using one.
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 and slightly up the sides of the prepared pan. Bake for 10 minutes, then set aside to cool completely.
03 - 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. Blend in the smooth peanut butter until fully incorporated.
04 - 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 to avoid incorporating excess air.
05 - Divide the filling mixture evenly into two separate bowls. Fold the melted dark chocolate into one half, stirring until the color is uniform. 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. Using a butter knife or offset spatula, draw slow, sweeping motions through both layers to create a marbled effect. Avoid over-mixing to maintain distinct swirls.
07 - Place the cheesecake in the center rack of the oven and bake for 50 to 60 minutes. The edges should be fully set and slightly puffed, while the center should still have a gentle jiggle when the pan is tapped. Do not overbake.
08 - Turn off the oven, crack the door open slightly, and let the cheesecake rest inside for 1 hour. This slow cooling process prevents cracks from forming on the surface.
09 - Transfer the cheesecake to the refrigerator and chill for at least 4 hours, or ideally overnight, until fully set and firm throughout.
10 - Heat the heavy cream in a small saucepan over medium heat until it begins to steam and small bubbles form around the edges. Remove from heat, add the chopped dark chocolate, and let sit for 1 minute. Stir until the ganache is glossy and smooth, then blend in the peanut butter until fully combined. Allow the mixture to cool slightly until it reaches a spreadable consistency.
11 - Spread the ganache topping evenly over the surface of the chilled cheesecake. Garnish with chopped roasted peanuts if desired. Slice with a clean, warm knife for neat portions and serve.