Preheat oven to 325F. In a large mixing bowl, mix sugar and flour. Set aside. In a small sauce pan, add 1 cup water, 1/2 lb margarine, 4 tablespoons cocoa. Bring to a boil. Once mixture boils, add buttermilk, soda, eggs, and vanilla. Mix thoroughly. Pour mixture over sugar and flour. Mix for 2 minutes with an electric mixer. Pour into a sheet cake pan (13 x 9 inch) and bake at 350F for 30 minutes. Remove and cool.
In a small sauce pan, mix margarine, cocoa and milk. Bring to a boil over low heat. Add confectioners sugar, pecans, and vanilla. Mix well and pour over cooled cake.
Cajun Country -- New Iberia, Louisiana