Preheat oven to 350°Line 22 cupcake cups with liners.
In a medium microwave-safe bowl, microwave butter until almost completely melted. Add dark chocolate and oil and microwave for 30 seconds. Stir. Microwave for an additional 15 seconds if necessary, until chocolate is completely melted. Stir until well combined and set aside to cool.
In a medium bowl, whisk together flour, cocoa powder, baking powder, baking soda, and salt. Set aside.
In a large bowl, whisk together sugar, eggs, and vanilla extract. Whisk in cooled chocolate mixture. (It can be warm, but if it is hot to the touch, set aside for another couple of minutes. You don't want to scramble the eggs!)
Whisk in half of the flour mixture until just combined. Add all of the buttermilk and mix. Whisk in the last of the flour, mixing until just combined.
Whisk in the coffee.
Fill cupcake tins just under 2/3 of the way full. You should have about 22 cupcakes. Don't over fill!
Bake for 15-18 minutes, until a toothpick inserted into the center of the cupcakes comes out clean.