In a saucepan, bring cocoa, 1 cup of buttermilk and margarine to a boil.
Pour over flour and sugar mixture.
Add eggs to the mixture and mix with a spoon (do not overmix)
Stir in the remaining ½ cup buttermilk and baking soda to the mixture.
Pour in an oiled and floured long cake pan and bake for 30 to 35 minutes. Cool 10 minutes before frosting.
Frosting:
Boil margarine, cocoa and milk. Pour over powdered sugar and mix well. Add vanilla and pecans. If frosting is too thick add a little more milk. Spread on top of still warm cake. Enjoy!!