In a food processor, pulse graham crackers until you get fine crumbs. Place crumbs in an 8x8-inch or 9x9-inch square baking dish. Melt butter and add it to the baking dish with the graham cracker crumbs. Mix together until all the crumbs are wet and press firmly onto the bottom of the dish. Bake at 350 degrees Fahrenheit for 12 to 15 minutes or until set and the edges are crisp.

In a food processor, blend cream cheese and sugar until smooth. Scrape bowl, then blend in eggs one at a time. Add sour cream and vanilla. Blend until incorporated. Remove 1 cup of the cheesecake batter into a separate bowl. Melt chocolate chips and add it to the 1 cup of cheesecake batter. Whisk until smooth and chocolate is incorporated. Set aside.

Add the peanut butter to the remaining cheesecake batter, still in the food processor bowl. Blend until smooth.

Spread half of the peanut butter cheesecake batter over the top of the cooked chocolate crust. Dollop the chocolate cheesecake batter and remaining peanut butter cheesecake batter over the peanut butter layer. Swirl with a knife until you achieve a desired marbled look. Tap the bottom of the pan against the counter to help the cheesecake batters settle.

Bake at 350 degrees Fahrenheit for 20 to 25 minutes or until edges are set. Turn oven off and leave the cheesecake in the oven for 1 hour. (This helps the cheesecake finish baking slowly to prevent cracks from forming, especially since we didn't use a water bath to bake the cheesecake in.)

Remove cheesecake from oven and allow to cool at room temperature for a couple of hours. Then lightly cover the pan with a lid or plastic wrap and refrigerate the cheesecake 4 hours to overnight. Keep refrigerated. Cut squares with a hot knife when ready to serve.