Preheat oven to 350 degrees. Prepare cupcake tin by adding cupcake liners.

In a medium saucepan on low heat, combine beer and butter and keep on low until butter dissolves.

Once butter is melted, slowly whisk in sugar, cocoa and espresso until they have completely dissolved.

Set mixture aside and allow to cool for at least 5 minutes (room temperature is fine but no hotter).

In the meantime, sift together flour, baking soda and salt in a small bowl, then set aside.

Mix together sour cream, vanilla, and eggs. Beat on low until combined then slowly blend the chocolate into the sour cream and eggs, keeping mixer speed on low.

Add flour one cup at a time and mix on medium speed until well blended but do not overmix.

Pour cupcake mixture into the prepared cupcake lines to about 3/4 full. Bake for 15-18 minutes or until a toothpick insert into the middle comes out clean.

Cool cupcakes in the pan for about 10 minutes, then remove them to a wire rack to finish cooling.

Combine the Bailey's and sugar in a saucepan and cook on medium until the mixture is reduced by half. Remove from heat and let cool completely before using.

Cream the softened butter in the bowl of a mixer. Gradually add the powdered sugar and mix until well combined.

Add the vanilla and mix thoroughly. Add the Irish Whiskey one Tablespoon at a time and combine thoroughly. If necessary add a bit more powdered sugar for correct consistency.

Spread on cupcakes with a knife or offset spatula or pipe using a piping bag and tip. Let the frosting set up a bit before drizzling with the Bailey's drizzle.