Preheat oven to 350. Mix together Miracle Whip, eggs, and water until well blended. Stir in browning mix, mixing just until moistened.
Coarsely chop two chocolate bars; stir into brownie mixture. Pour into greased 13x9 inch pan.
Bake 30-35 minutes or until edges begin to pull away from sides of pan. Immediately top with 1 chopped chocolate bar. Let stand about 5 minutes or until melted; spread evenly over brownies. Garnish with nut halves, if desired.