Preheat oven to 350 degrees.
Grease and flour a 13 X 9 inch pan.
In a large mixer bowl combine the flour, sugar, cocoa, baking soda and salt, blending well.
Blend in the butter, sour cream, eggs, and vanilla.
Beat 3 minutes on medium speed.
Pour batter into prepared pans and bake 40 - 45 minutes or until cake tests done.
Cool in pan on a wire rack.

Fudge Frosting:
In a small saucepan over low heat, melt butter.
Add cocoa and cook, stirring constantly, until the mixture begins to boil.
Pour mixture into a small mixer bowl and allow to cool completely.
Add the powdered sugar to cocoa mixture alternately with milk.
Beat to a spreading consistency.
Blend in vanilla.
Frost cake when cool.