In a large saucepan, combine the mangoes, sugar and cinnamon. Cook and stir until mixture comes to a boil. Combine cornstarch and water until smooth; stir into pan. Cook and stir for 2 minutes or until thickened. Transfer to a greased 11x7-in. baking dish. Dot with butter.
In a small bowl, combine flour and sugar. Cut in shortening until mixture resembles coarse crumbs. Stir in milk; mix well. Drop by tablespoonfuls onto hot fruit. Bake, uncovered, at 400° for 20-25 minutes or until bubbly and golden brown. Serve warm.