In saucepan over medium heat combine the sugar, butter, and water; bring just to the boiling point, stirring constantly. Remove from heat; stir in chocolate and vanilla, stirring until chocolate is melted and mixture is smooth.
Add eggs one at a time, beating well after each addition.
Sift together the flour, baking soda, and salt; stir into chocolate mixture. Stir in about half of the chopped pecans or walnuts. Transfer to a greased and floured 8-inch square baking pan. Sprinkle with remaining chopped pecans or walnuts. Bake at 325° for 25 minutes, or until edges are firm. Center will be shiny. Cool on rack in pan. Cut into squares.
Makes about 16 brownies.