Cream the one third cup butter and sugar together, add the well beaten eggs and mix well. Sift flour and baking powder and add alternately with the milk to the first mixture. Put one third of mixture into a bowl and add the 1 Tablespoon of butter and chocolate which have been melted together. To the white batter, add the vanilla. Drop white batter, then chocolate, by spoonfuls into a well-greased, deep cake pan and bake at 350-F about 40 minutes.