Pre-Heat oven to 325 degrees. Line a 24 cup mini muffin pan with paper liners.
Combine the chocolate, cocoa powder and brown sugar in a large bowl, add hot coffee and whisk together. Let cook to room temperature.
Whisk the flour, granulated sugar, salt and baking soda into a medium bowl.
Whisk the egg, egg yolk, vegetable oil, buttermilk and vanilla into the melted chocolate mixture. Add the flour mixture and whisk and until smooth.
Spoon a tablespoon of batter into each muffin cup (just a little past the half way point). Bake until a toothpick inserted into centers comes out clean, about 15 minutes.
Fill a large bowl halfway up with ice water.
Combine heavy cream, corn syrup, butter and salt in a medium saucepan and bring to simmer. Remove form the heat, add the chocolate and whisk until smooth let cool to room temperature.
Carefully place in ice water and let sit stirring every couple of minutes, until frosting is thick enough to spread. About 15 minutes.
Spread frosting on cupcakes (whether using a piping bag or just spreading a little on each cupcake).
Eat...... err I mean serve =)