Preheat oven to 325 degrees F. Lightly grease and flour a 9-inch-square pan. Beat shortening and sugar with an electric mixer at medium speed until creamy, about 3 minutes. Add egg and molasses, beating well. Combine flour and next five ingredients. Turn mixer down to low speed and gradually add dry ingredients, mixing until blended. Gradually add boiling water, mixing until blended. Spoon batter into baking pan. Bake 35 to 40 minutes, or until a wooden pick inserted in the center comes out clean. Sprinkle with powdered sugar. Serve warm.