Preheat oven to 350 degrees F (175 degrees C). Grease a 13 x 18 inch sheet pan with butter then dust lightly with flour.

In a large sauce pan, over low heat, melt 3 sticks butter. When the butter is melted add 1 ½ cups water and whisk in 1/4 cup plus 3 tablespoons cocoa powder. Bring the mixture to a boil then remove from heat. Allow the cocoa mixture to cool slightly.

Meanwhile, in a large bowl, combine 3 cups all purpose flour, 3 cups sugar, 1 ½ teaspoon baking soda and ¾ teaspoon salt.  Stir to mix. 

Add the cocoa mixture to the dry mixture, stirring continuously, until blended.

In a small bowl, beat together 3 eggs and ¾ cup sour cream until combined.   Slowly add the egg mixture to the large bowl containing the cocoa and flour mixture.

Pour batter into prepared pan. Bake for 20 minutes.  At 20 minutes check and continuing baking until a toothpick inserted into the center comes out clean.

When there is 10 minutes baking time left on the cake, make the frosting. In a large saucepan, over low heat, add ½ cup milk and 1 1/2 sticks butter. When melted, remove from heat and slowly whisk in ¼ cup plus 3 tablespoons cocoa until combined.  Stir in 4 cups confectioners' sugar and 1 ½ teaspoon vanilla, then fold in the nuts, mixing until blended. When the cake comes out of the oven, spread frosting over hot or warm cake.

Can be made and frosted and kept at room temperature for up to 3 days. Cover it lightly with plastic wrap to protect it from dust, etc. Cakes both frosted and unfrosted, cut and un-cut, are perfectly fine at room temperature for several days. Refrigeration is only necessary if your kitchen gets very hot during the day (think bacteria feeding frenzy) or if you're making a cake that won't be served for more than three days.

To refrigerate, wrap unfrosted cakes in plastic to protect it from absorbing any weird fridge smells and to protect it from drying out, and then unwrap it to warm up on the counter before serving. For frosted cakes, chill the cake uncovered for fifteen minutes to harden the icing, then wrap it in plastic wrap.

Preheat oven to 350 degrees F (175 degrees C). Grease a 10" x 15" or 11" x 15" inch sheet pan with butter then dust lightly with flour.

In a large sauce pan, over low heat, melt 2 sticks butter. When the butter is melted add 1 cup water and whisk in 5 tablespoons cocoa powder. Bring the mixture to a boil then remove from heat. Allow the cocoa mixture to cool slightly.

Meanwhile, in a large bowl, combine 2 cups all purpose flour, 2 cups sugar, 1 teaspoon baking soda and 1/2 teaspoon salt. Stir to mix.

Add the cocoa mixture to the dry mixture, stirring continuously, until blended.

In a small bowl, beat together 2 eggs and 1/2 cup sour cream until combined. Slowly add the egg mixture to the large bowl containing the cocoa and flour mixture.

Pour batter into prepared pan. Bake for 20 minutes. At 20 minutes check and continuing baking until a toothpick inserted into the center comes out clean.

When there is 10 minutes baking time left on the cake, make the frosting. In a large saucepan, over low heat, add 1/4 cup plus 2 tablespoons milk and 1 stick butter.  When melted, remove from heat and slowly whisk in ¼ cup plus 1 tablespoon cocoa until combined. Stir in 4 cups confectioners' sugar and 1 ½ teaspoon vanilla, then fold in the nuts, mixing until blended. When the cake comes out of the oven, spread frosting over hot or warm cake.