In a large bowl combine the flour, sugar, baking soda, and salt. .
Mix in sour cream (spoon or electric beater). Beat in the eggs. Set aside.
In a saucepan, melt the butter, then stir in the water and cocoa. Bring mixture to a boil, then remove from heat. Allow to cool slightly, then stir cocoa mixture into the sour cream mixture, mixing with large spoon or electric handheld beater, until blended.
Pour batter into prepared sheet pan.
Bake at 350 F for 20 minutes, or until a toothpick inserted into the center comes out clean.
Icing
In a large saucepan, combine the milk, cocoa and butter. Bring to a boil, and remove from heat.
Stir in the confectioners’ sugar and vanilla, then fold in the nuts, mixing until blended.
Spread frosting over hot cake as soon as you remove it from the oven. This is imperative!
Notes
This cake can serves from 20 to 35 depending on your preferred sized servings.