Preheat oven to 350F. In large bowl of a standard mixer, combine sugar, flour and salt and let sit. In a small saucepan, bring 2 sticks butter, water and cocoa to a boil.
Take from heat and immediately pour over your dry mix in the bowl and combine well. Then add your cold sour cream, eggs and baking soda. Mix completely then pour into a greased and floured 11 1/2 x 15 1/2inch baking sheet.
Bake at 350 for 30 minutes or until center of brownies test done with a toothpick. Frosting-Boil milk, butter, and cocoa until bubbly. Remove from heat and add nuts, vanilla, and powdered sugar. Mix until smooth and spread on warm brownies. Let frosting set before serving.