Preheat the oven to 350 F (180 C) and line a muffin tin with 8 paper liners.

Using an electric mixer, cream the butter and sugar, then add the egg and mix well.
Combine the flour, cocoa, baking powder, and salt, then add them to the previous mixture, alternating with the Guinness and yogurt.
Mix well until a homogeneous texture is obtained.

Fill the paper liners with the preparation, then bake for 25 minutes or until a toothpick inserted in the center comes out clean.
Let cool for 5 minutes, then transfer the cupcakes to a cooling rack.

Glaze: Cream the butter using an electric mixer, then gradually add the powdered sugar, alternating with the Bailey’s.
Put the preparation in a piping bag with a star tip, then frost the cooled cupcakes with the glaze.