Preheat oven to 350°F (175°C). Grease a 13×18-inch sheet cake or jelly roll pan.

In a saucepan, combine 1 cup butter, 1 cup water, and 1/4 cup cocoa powder. Heat over medium until smooth. Do not let it boil for too long.

In a large bowl, whisk together 2 cups sugar, 2 cups flour, and 1/8 teaspoon salt.

Pour the hot butter mixture into the dry ingredients, stirring continuously.

Beat in 2 large eggs, one at a time, then add 1 teaspoon baking soda and mix well.

Add 1/2 cup sour cream and 1 teaspoon vanilla extract, mixing until smooth.

Spread batter in the prepared pan and bake for 20 minutes or until a toothpick comes out clean.

In a saucepan, combine 1/2 cup butter, 1/4 cup cocoa powder, and 1/4 cup + 2 tablespoons milk. Heat over medium until it reaches a boil, then remove from heat.

Stir in the sifted confectioners' sugar and 1/2 teaspoon vanilla extract until smooth.

Stir in chopped pecans or sprinkle them on top after spreading the icing, if desired.

Pour the warm icing over the hot cake, spreading evenly to let it seep into the cake.

Let the cake cool completely in the pan before slicing and serving.