Cream butter. Add sugar and molasses. Beat until light. Add egg and beat well.
Sift dry ingredients together and use a small amount to coat berries. Add remainder alternately with hot water to first mixture, beating until smooth. Fold in floured blueberries.
Bake in greased and floured 13-inch by 9-inch 3-inch pan at 350 degrees for about 35 minutes.
Serve hot or cold with blueberry sauce.