Follow the directions for preparing yellow cake mix, substituting water and/or milk with beer. Bake according to directions for cupcakes. Allow cupcakes to cool for at least 10 minutes before frosting.
While cupcakes are baking, using an electric beater, beat melted butter until creamy and foamy. Mix in sake. Slowly add in confectioner's sugar, one cup at a time. Let frosting sit for at least 10 minutes to become stiff.
Use a piping kit (I used Wilton's 1M tip) to frost cooled cupcakes.
Notes
Most of the beer flavors evaporate during the baking process, but darker beers will retain a decent beer taste.