Grease a 13- x 9- x 2-inch baking pan; sprinkle brown sugar evenly over bottom of pan. Drain cherries, reserving juice for Cherry Sauce; add enough water to juice to equal 1 1/2 cups. Set aside. Spoon cherries evenly over brown sugar. Set aside.
Cream shortening; gradually add sugar, beating well. Add egg, beating well. Combine flour, baking powder, and salt; add to creamed mixture alternately with milk, beginning and ending with flour mixture. Stir in vanilla.
Pour batter over cherries in pan. Bake at 350° for 40 minutes or until a wooden pick inserted in center comes out clean. Cut into squares, and spoon Cherry Sauce over top. Garnish with whipped cream.