Cream 1 cup sugar with butter; add flour, baking powder, salt and milk; mix well.
Pour into 12 x 8 x 2 inch baking pan. Pour blackberries over batter. Sprinkle remaining sugar over berries. Pour boiling water over top.
Bake at 350° for 50 minutes or until golden brown.
Serve plain or with cream.
Please Note: Nutritional values listed may vary from final results depending on actual measurements and brands used to prepare the recipe.