01 - Preheat the oven to 325°F (160°C). Grease a 9-inch (23 cm) springform pan and line the bottom with parchment paper. Wrap the outside of the pan tightly with aluminum foil if using a water bath.
02 - Combine the crushed chocolate sandwich cookie crumbs with the melted butter in a medium bowl, stirring until the mixture resembles wet sand. Press the crumb mixture firmly and evenly into the bottom of the prepared springform pan, working it slightly up the sides. Bake for 10 minutes, then set aside to cool while preparing the filling.
03 - Using a stand mixer or hand mixer fitted with the paddle attachment, beat the softened cream cheese and granulated sugar on medium speed until completely smooth and free of lumps, scraping the bowl as needed. Add the smooth peanut butter and blend until fully incorporated.
04 - Reduce mixer speed to low. Add the eggs one at a time, beating briefly after each addition just until combined — avoid overmixing to prevent air pockets. Blend in the vanilla extract and sour cream until the mixture is silky and uniform.
05 - Divide the filling mixture evenly between two bowls. Into one half, fold the melted and slightly cooled dark chocolate until the batter is uniformly colored. Leave the other half as the plain peanut butter mixture.
06 - Pour the chocolate cheesecake batter over the cooled crust and spread into an even layer. Gently spoon the peanut butter batter on top in dollops. Using a butter knife or thin spatula, draw swirling motions through both layers to create a marbled effect — do not over-swirl or the pattern will muddy.
07 - Place the cheesecake on the center rack and bake for 50–60 minutes. The edges should be set and lightly golden while the center still has a subtle jiggle when gently shaken. Avoid opening the oven door during baking.
08 - Once baked, turn off the oven and crack the oven door open about an inch. Let the cheesecake rest inside the cooling oven for 1 hour. This slow cooling helps prevent cracks from forming on the surface.
09 - Transfer the cheesecake to a wire rack and cool to room temperature. Then cover loosely with plastic wrap and refrigerate for at least 4 hours, preferably overnight, until the filling is fully set and firm.
10 - In a small saucepan, heat the heavy cream over medium-low heat until it begins to steam — do not let it boil. Remove from heat and add the chopped dark chocolate, letting it sit undisturbed for 1 minute. Stir gently from the center outward until a glossy ganache forms. Stir in the creamy peanut butter until smooth. Allow the topping to cool and thicken slightly for 5–10 minutes.
11 - Spread the ganache topping evenly over the chilled cheesecake. Scatter chopped roasted peanuts over the surface if desired. Slice with a sharp knife dipped in hot water and wiped clean between cuts for clean portions. Serve chilled.