Crust: Preheat the oven to 350º F. Line a regular-sized muffin pan with paper muffin liners. Mix graham cracker crumbs and melted butter until it resembles coarse sand. Distribute 1-2 tbsp of crumbs in each muffin cup. Press the crumbs down firmly into the pan using a 1/3 cup measure. Bake for 5 minutes, then remove from the oven and allow to cool.
Cheesecake: In a mixing bowl, beat the cream cheese, peanut butter, and sugar with an electric mixer until smooth, about 1-2 minutes. Add vanilla extract and eggs, one at a time, mixing just until the yolk breaks to avoid over beating. Divide the cheesecake batter evenly among the muffin cups, filling each full. Bake for 15-17 minutes or until the center is slightly jiggly. Allow to cool to room temperature, then chill in the fridge for at least 4 hours.
Chocolate Ganache: Place chocolate chips in a medium bowl. Heat the heavy cream in a small pot over low heat until just before boiling. Pour over the chocolate chips, let stand for 1-2 minutes, then stir until smooth. Let ganache come to room temperature before spooning onto each cheesecake. Top with chocolate shavings.