In a large bowl, cream the shortening and 1/2 cup sugar until light and fluffy. Add the egg and mix well. Combine 2 cups flour, baking powder and salt; add to the creamed mixture alternately with the milk, beating well after each addition.
Spread into a greased 9-in. square baking dish. Toss the blackberries with lemon juice; sprinkle over batter. In a small bowl, combine the cinnamon and remaining sugar and flour; cut in the butter until mixture resembles coarse crumbs. Sprinkle over berries.
Bake, uncovered, at 350° for 45-50 minutes or until a toothpick inserted in the center comes out clean. Refrigerate leftovers.