Make a paste of the cocoa, food coloring, and salt - set aside.
Mix buttermilk and vanilla - set aside.
Cream butter, add sugar gradually. Then add eggs and cocoa paste.
Add flour gradually, alternate with the milk mixture.
Fold in baking soda and vinegar (DO NOT BEAT AFTER THIS!)
Bake in 2 (9 inch) pans 30-35 minutes at 350° or until toothpick inserted comes out clean.
Over low heat cook together flour and milk. Continue to stir to remove lumps.
Cook together until like rubber. Set aside and cool.
Cream butter, sugar, and vanilla (soften the butter first, do not melt it)
Add cooled flour mixture and frost cake