Preheat your oven to 350 degrees F. Grease a 9-inch round spring form pan with butter and set it aside.
In a blender or food processor, grind the graham crackers into fine crumbs. Add the melted butter and pulse until the mixture resembles damp sand. Press the graham cracker crumbs and butter mixture into the bottom of the greased pan in an even layer. Bake for 10 minutes. Remove the pan and allow it to cool completely before adding the cheesecake batter.
Melt the chocolate in a double boiler until smooth. Allow the chocolate to cool slightly
In the bowl of a stand mixer, cream the room temperature cream cheese on medium speed until smooth and fluffy, or about 5 minutes. Add the sugar, sour cream, eggs, vanilla, melted chocolate, and Guinness. Mix until everything is well combined. Scrape down the bowl, making sure to get the bottom, and mix again for a few more minutes.
Pour the cheesecake batter over the crust. Smooth the top with a spatula. Place the cheesecake in the oven.
Bake for 60 minutes. After that time, turn off the oven, crack the door slightly, and allow the cheesecake to rest in the oven for another 60 minutes. After that, remove it to a wire rack and allow it to cool completely. Cover and stash in the fridge overnight.
Once the cheesecake has fully cooled, make the ganache. Add the chopped chocolate and heavy cream to a microwave safe bowl. Microwave in 30 second increments until the chocolate has melted completely into the cream. Whisk to combine.
Add the room temperature butter and the whiskey. Whisk to combine. Let the ganache cool and thicken slightly. Pour it on top of the cheesecake.