Preheat your oven to 350°F (175°C). Line a cupcake pan with eight paper liners.

In a small saucepan, add about an inch of water and bring to a simmer. Turn off the heat and place a heatproof bowl over the pan. Add the chopped semisweet chocolate to the bowl and allow it to melt until smooth. Remove from heat and let it cool for about 10 minutes.

In a medium bowl, sift together the all-purpose flour and cocoa powder. Stir in the baking soda, espresso powder, and salt.

In a large mixing bowl, beat together the softened butter, brown sugar, and granulated sugar until light and creamy, about 1-2 minutes.

Scrape down the bowl, then add the egg and peppermint extract. Beat in the melted chocolate until fully incorporated.

In a measuring cup, mix the buttermilk and hot coffee until combined.

Gradually add the flour mixture to the chocolate mixture, alternating with the buttermilk mixture. Start and end with the dry ingredients.

Transfer the batter into the lined cupcake liners, filling each about halfway. Bake for 18-20 minutes or until a toothpick inserted comes out with a few crumbs. Cool for about 15 minutes before transferring to a wire rack.

Once completely cool, decorate generously with mint frosting. Store at room temperature for up to three days or refrigerate for up to one week.