Preheat your oven to 350 degrees Fahrenheit.
Line a standard-size muffin pan with cupcake liners.
Chop the bittersweet chocolate and place it in a medium bowl along with the cocoa powder.
Pour hot coffee over the chocolate and cocoa mixture. Whisk until smooth.
Refrigerate mixture for 20 minutes.
In another bowl, whisk the flour, sugar, salt, and baking soda together.
In the cooled chocolate mixture, whisk in the vegetable oil, eggs, vinegar, and vanilla extract until smooth.
Add the dry mixture to the chocolate mixture, whisking until smooth.
Divide the batter evenly into the muffin pan cups.
Bake for 17 to 19 minutes until firm to the touch.
Cool the cupcakes in the pan for 10 minutes before transferring them to a wire rack.
In a stand mixer, whip the butter on medium-high speed for 5 minutes.
Gradually add the powdered sugar, mixing until incorporated.
Increase speed and add vanilla, whipping until light and fluffy.
Frost the cupcakes as desired.
