In a large bowl, combine the first five ingredients. Add the water, oil, vanilla and vinegar; mix well (batter will be thin).
Pour into a greased 13-in. x 9-in. baking pan. Bake at 350° for 25-30 minutes or until a toothpick inserted near the center comes out clean. Cool completely.
For frosting, in a large bowl, beat cream cheese and butter until fluffy. Add the confectioners’ sugar, cocoa, salt, milk and vanilla; mix well. Spread over cake. Store in the refrigerator.