01 - Preheat oven to 325°F. Grease a 9-inch springform pan and line the bottom with parchment paper.
02 - Combine the crushed chocolate cookie crumbs with the melted butter, stirring 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 on medium speed until completely smooth and lump-free. Add the 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. 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. Into one half, fold the melted dark chocolate 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 on top in dollops. Run a butter knife or skewer through the batter in gentle figure-eight motions to create a marbled pattern.
07 - Place the cheesecake in the center of the oven and bake for 50 to 60 minutes. The edges should be fully set while the center retains a slight jiggle when the pan is gently shaken.
08 - Turn off the oven, crack the door open a few inches, and leave the cheesecake inside for 1 hour. This gradual cooling 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. Remove from heat, add the chopped dark chocolate, and stir until silky smooth. Stir in the peanut butter until well blended. Let the mixture cool slightly until it reaches a spreadable consistency.
11 - Spread the ganache topping evenly over the chilled cheesecake. Garnish with chopped roasted peanuts if desired. Slice into 12 portions using a sharp knife dipped in hot water and wiped clean between cuts.