Turn oven to 350°F. Grease the sheet pan.
In a bowl, mix flour, sugar, salt, and baking soda.
In a saucepan, melt butter with water and cocoa.
Let it boil. Then remove from heat.
Pour the cocoa mix into the flour. Stir well.
Add buttermilk, eggs, and vanilla. Mix well.
Pour this mix into your pan. Spread it evenly.
Bake for 20 minutes or until the middle is set.
While the cake bakes, make the icing.
Melt butter. Add cocoa and milk. Heat gently.
Remove from heat. Add sugar and vanilla. Stir.
Add pecans if you want. Mix until smooth.
Pour warm icing on the hot cake. Spread fast.
Let the cake cool. Cut into pieces and serve.