For the cake, in a mixing bowl, cream sugar and butter. Add eggs; beat well. Combine dry ingredients; add to creamed mixture alternately with buttermilk. Mix well. Pour into a greased and floured 13x9x2" baking pan. Bake at 350 degrees for 35-40 minutes or until the cake tests done. Cool.
For frosting, cream shortening and butter in a mixing bowl. Add vanilla. Gradually beat in sugar. Add milk; beat until light and fluffy. Frost cake.