Preheat the oven to 350 degrees F. Grease a 10-inch springform pan liberally with softened butter (a 9-inch springform pan will also work but the results will look slightly different from the photos). Wrap the pan with aluminum foil on the bottom and up the sides.
Break the graham crackers into a food processor. Pulse the machine several times to create crumbs, and then slowly add the melted butter with the food processor running. The mixture should resemble wet sand.
Press the mixture firmly into the bottom of the prepared pan and bake for 10 minutes. Set aside, and then lower the oven temperature to 325 degrees F.
In a stand mixer fitted with the paddle attachment (or with a large bowl and an electric hand mixer), combine the cream cheese, peanut butter, sugar and sour cream on medium speed until smooth. Add the eggs, one at a time, followed by the vanilla extract.
Pour the filling into the springform pan, using a spatula to even out the top. Place the pan in a large roasting dish. Fill the pan with 1-2 inches of hot water (note: I find the easiest way to do this without creating any spills is to fill a large liquid measuring cup with hot water, place the roasting pan in the oven, and then carefully and quickly add the water right before closing the oven door).
Bake the cheesecake until the center is almost completely set, approximately 70-80 minutes.
Carefully remove from the oven. Place on a cooling rack in the refrigerator for 4 hours, or up to overnight. Once the cake is cool, remove the foil from the springform pan. Use a knife or offset spatula to carefully draw between the cheesecake and the pan, dislodging any areas that may have stuck before removing the sides of the springform pan.
To prepare the ganache, place the bittersweet chocolate and butter in a medium-sized heatproof bowl over a pot of simmering water. Using a heatproof spatula, stir the mixture until melted and smooth. Allow the glaze to cool for 2-3 minutes until it starts to thicken up slightly. Starting at the center and moving outward in a circular motion, pour glaze over the chilled cheesecake, smoothing the top with a spatula.
Because the chocolate ganache hardens when cold, I think this cake is best served at room temperature.