Step 1

Preheat oven to 350 degrees F (175 degrees C). Grease and flour a 10x15 inch pan.

Step 2

Combine the flour, sugar, baking soda and salt. Beat in the sour cream and eggs. Set aside. Melt the butter on low in a saucepan, add the water and 5 tablespoons cocoa. Bring mixture to a boil then remove from heat. Allow to cool slightly, then stir cocoa mixture into the egg mixture, mixing until blended.

Step 3

Pour batter into prepared pan. Bake in the preheated oven for 20 minutes, or until a toothpick inserted into the center comes out clean.

Step 4

For the icing: In a large saucepan, combine the milk, 5 tablespoons cocoa and 1/2 cup butter. Bring to a boil, then remove from heat. Stir in the confectioners' sugar and vanilla, then fold in the nuts, mixing until blended. Spread frosting over warm cake.