To prepare cake: Preheat oven to 375 degrees. Grease and lightly flour a 9 x 13 inch baking pan; set aside.

In a large bowl, mix together flour, granulated sugar, bakingn soda, and salt; set aside.

In a medium saucepan, bring butter, water, and cocoa powder to a boil over medium-high heat, stirring frequently, until butter melts. Add the butter mixture, the sour cream, eggs, and vanilla to the flour mixture and stir with a wooden spoon until all of the four is moistened.

Pour the batter into the pan and spread smooth. Bake 30 min., or until a toothpick inserted into the center comes out clean.

To prepare icing: While the cake is baking, in a medium saucepan, bring butter, milk, and cocoa powder to a boil over medium heat; remove from heat. With a wooden spoon, stir in confectioners' sugar, chopped pecans and vanilla, until all of the sugar is moistened.

Spread the icing on the cake as soon as it is removed from the oven. Cool completely in the pan on a wire rack. Cut into squares and serve.