The cake:
http://www.epicurious.com/recipes/recipe_views/views/107105
and use Guiness, and Hershey’s Dark cocoa powder for the cake.  Skip the icing part of that recipe.  Spray some Pam (or Pam for Baking) into the cupcake papers,  fill them about 3/4 of the way, and cook it for a shorter amount of time.  Test with a toothpick.

The frosting:
From The Joy of Cooking (1997), “Quick White Frosting I”, using 3 tbsp hot heavy cream instead of 4 tbsp butter.  Instead of coffee/whatever, using 2 tbsp of Jameson’s 12-year-old whiskey, and 2 tbsp Baileys.

The 75th Anniversay Edition doesn’t quite have this recipe, so here’s the full deale:
2+ c confectioner’s/powdered sugar
3 tbsp hot heavy cream
2 tbsp Jameson 12-year whiskey
2 tbsp Bailey’s
1 tsp Vanilla extract
pinch of salt

Heat heavy cream in tiny pot, or possibly a metal measuring cup.  Beat the heavy cream into 2c confectioner’s sugar.  When well-mixed, beat in everything else, one at a time.  Add more sugar and until it’s thick enough and tastes right.