Cream margarine and sugar; beat in egg. Add dry ingredients alternately with applesauce, beating till blended. Fold in blueberries. Pour into a 6 cup greased and floured mold, or 9x13-inch baking dish. Bake at 350^ for about 1 hour and 10 minutes. Test near center with toothpick for doneness.
Decorate with lemon sauce and candied fruit if desired.
Mix sugar, cornstarch and salt. Slowly stir in water and slightly beaten egg. Cook and stir till mixture thickens. Remove from heat; stir in lemon peel and lemon juice. Serve warm over warm cake.