Cream the 1/3 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 1/3 of mixture into a bowl and add the 1 Tbsp 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.