Mix sugar, flour, salt, baking powder and cocoa together in a 9-inch square baking pan. Stir in milk, butter and vanilla. Spread batter in pan.
For topping: Combine white and brown sugars and cocoa and sprinkle over batter. Pour water over top.
Bake at 350 degrees for 45 minutes or until top springs back when lightly touched. Serve warm or cool with cream, sour cream or whipped topping. Serves 6 to 8.
Note: "Recipe can easily be doubled and use 13x9-pan."