1. Preheat the oven to 350°F and line a 12-cup muffin pan with cupcake liners.

2. In a large bowl, whisk together the flour, cocoa powder, granulated sugar, brown sugar, baking powder, baking soda, and salt.

3. Add the eggs, buttermilk, vegetable oil, and vanilla extract, then mix until combined.

4. Slowly pour in the hot coffee and stir until the batter is smooth and thin.

5. Divide the batter evenly among the cupcake liners, filling each about two-thirds full.

6. Bake for 18 to 22 minutes, or until a toothpick inserted in the center comes out with a few moist crumbs.

7. Let the cupcakes cool in the pan for 5 minutes, then transfer to a wire rack and cool completely.

8. To make the frosting, beat the butter until creamy.

9. Add the powdered sugar, cocoa powder, melted semisweet chocolate, heavy cream, vanilla extract, and salt. Beat until smooth and fluffy.

10. Pipe or spread the frosting onto the cooled cupcakes and serve.