place 12 individual paper cases in a shallow muffin pan
place all of the ingredients for the cakes, except for the melted chocolate, in a large mixing bowl, and beat with an electric mixer until the mixture is just smooth
beat in the melted chocolate, stirring until well blended
spoon equal amounts of the mixture into each paper case, filling them three-quarters full
bake in a preheated oven, 350 F / 180 C, for 15 minutes or until springy to the touch
transfer the chocolate cakes to a wire rack and let them cool completely
meanwhile, make the lemon butter cream
place the butter in a mixing bowl and beat until fluffy, then gradually beat in the confectioners' sugar
beat in the lemon rind and gradually add the lemon juice, beating well
when cold, cut the top off each cake using a serrated knife
cut each cake top in half
spread or pipe the butter cream over the cut surface of each cake top and push the 2 cut pieces of cake top into the frosting to form wings