Preheat oven to 300º
Combine- flour, sugar, soda, salt
Melt margarine in saucepan, add cocoa and water (medium heat) – bring to a boil and remove from heat
Pour the hot ingredients over the flour mixture.
Add eggs and buttermilk
Pour into greased and floured pan 15x12x2
Bake 300 for 30 minutes
Prepare fudge frosting-
Combine butter, buttermilk and cocoa in saucepan.
Bring to a boil.
Remove from heat.
Add – powdered sugar and vanilla
Spread over cake while still warm and in same pan.