Cream butter, add sugar slowly and beat well. Add the egg yolks one at a time, beating well after each addition.
Add the chocolate which has been melted over low heat and cooled. Beat until smooth.
Sift together three times the flour, baking powder, soda and salt. Add to the butter alternately with the beer, a little at a time, and blend well.
Beat the egg whites until stiff but not dry and fold in.
Bake in a buttered loaf pan (9×5×3) about 30 minutes in a preheated 375° oven plain or frost with a frosting.