Preheat the oven to 325 F. Spray a deep 9-inch springform pan with nonstick cooking spray. Wrap aluminum foil tightly around the outside of the pan, coming up to the top edge. I like to use heavy-duty 18-inch foil, to prevent any water from leaking in to the cheesecake, but if you don’t have 18-inch foil, consider doing 2 overlapping layers of foil to make it more waterproof. Put water on to boil for a water bath.
Place the chocolate graham crackers in a food processor and process them until they’re fine crumbs. (Alternately, you can put them in a plastic bag and crush them with a rolling pin until they’re crumbs.) Melt the butter in the microwave, and stir the butter and crumbs together until the crumbs are the texture of wet sand.
Firmly press the chocolate crumbs into the bottom and up the sides of the springform pan, then refrigerate the pan while you prepare the filling.
Place the room temperature cream cheese in the bowl of a large stand mixer fitted with a paddle attachment. (A hand mixer can also be used.) Beat the cream cheese on medium speed until it is fluffy and free of lumps. Add the brown sugar and mix it in, then scrape down the bottom and sides of the bowl well.
Mix in the peanut butter, vanilla, and salt, and mix on medium-low speed until well-incorporated. With the mixer running on low, slowly stream in the International Delight REESE'S Peanut Butter Cups Creamer and 4 ounces of whipping cream.
Finally, stop the mixer and add the lightly beaten eggs. Stir these in by hand with a spatula. At first the mixture will look separated, but keep stirring and it will all come together in a smooth, silky batter.
Melt the semi-sweet chocolate in the microwave. Divide the peanut butter cheesecake batter in half, and add the melted chocolate to one half, stirring until smooth and homogenous. Separate out 1 cup of chocolate batter (about 4.5 oz) and place it in a piping bag.
To make the striped interior effect, take a large ice cream scoop and place two scoops of peanut butter cheesecake in the center of the prepared pan. Place two scoops of chocolate cheesecake right on top of it—this will push down on the peanut butter cheesecake and cause it to spread out. Continue this layering, making concentric circles with the two batters, until you’ve used all the chocolate cheesecake and have only a little peanut butter cheesecake remaining. Spread the remaining peanut butter cheesecake on top and smooth it into an even layer.
Pipe lines of chocolate cheesecake across the top of the peanut butter cheesecake. Take a toothpick and drag it through the lines, from top to bottom, then move over about half an inch and drag it in the opposite direction, from bottom to top. Continue this pattern across the whole cheesecake.
Place the springform pan inside a larger cake pan or roasting dish. Carefully pour the boiling water in larger pan, coming halfway up the sides of the cheesecake pan.
Bake at 325 F for 90 – 100 minutes. After an hour, I like to cover the top with very loosely tented foil so that it doesn’t get too dark. The cheesecake should appear set around the edges but still jiggle in the middle when the pan is tapped—it will firm up as it sits in the oven and rests in the refrigerator overnight. If it does not move when you tap it, it is overbaked.
Once done, turn the oven off but keep the cheesecake in the cooling oven for 1 hour. After an hour, carefully remove it from the water bath, peel off the foil, and refrigerate the cheesecake for at least 4 hours. (Overnight is good, too!)
Release the sides of the pan, and run a thin metal spatula under the crust to remove it from the bottom. Slide the cheesecake onto a serving plate.
Combine ¾ cup cream with ¼ cup powdered sugar and whip to firm peaks. Transfer to a piping bag fitted with a large star tip, and pipe rosettes of whipped cream all along the outside edge of the cheesecake. Decorate the whipped cream with chocolate shavings and peanut butter cups.
For the cleanest cuts, cut the cake when it is still cool, and wipe the knife off between cuts. Store the Chocolate Peanut Butter Cheesecake in the refrigerator for up to a week, and for the best taste and texture, let it sit at room temperature for 10-15 minutes before serving so it loses some of the refrigerator chill.