Cake
Preheat oven to 350 degrees. Grease a 9 x 13 pan.
In a saucepan, combine butter, water, and cocoa over medium heat until butter melts.
In a bowl, mix sugar, flour, salt, eggs, baking soda, sour cream, and vanilla.
Pour the warm cocoa mixture into the dry mixture and stir until smooth.
Pour batter into prepared pan.
Bake for 20 minutes.
Frosting
Combine butter, cocoa, and milk in a saucepan and bring to a boil.
Remove from heat.
Add vanilla and confectioners sugar. Mix with a hand mixer until smooth.
Pour frosting over hot cake.
Sprinkle with pecans.