Preheat oven to 350º.
Combine sugar, flour and salt in a large bowl. Set aside
In a saucepan, add 2 sticks of butter, 4 tablespoons of cocoa and 1 cup of water. Bring to a boil.
In a small bowl, beat together 2 eggs, 1 teaspoon vanilla, baking soda and sour cream.
Combine all 3 mixtures into one and whisk together.
Spray a half sheet pan (one of my Top 11 Kitchen Accessories I Can’t Live Without) with a cooking spray. Pour mixture into pan and place in preheated oven. Bake for 20-30 minutes until center is done and toothpick comes out clean.
While cake is baking, make the frosting.
Heat 1 stick butter, 6 tablespoons of milk and 4 tablespoons cocoa until butter is melted (I did mine in a microwave for ease). Pour into medium sized bowl. Add 4 cups of powdered sugar, 1 teaspoon vanilla and chopped nuts. Mix well together with a whisk.
When cake is done, let stand for 5 minutes. Pour frosting over the top and cover whole top (do it after the 5 minutes so that some of the frosting soaks into the cake). Let cake cool. Cut and serve.