Cream together butter and sugar; add eggs and vanilla. Set aside. Mix together food coloring, cocoa, vinegar and baking soda. Stir in buttermilk and add to sugar/butter mixture.
Sift cake flour and salt. Add creamed mixture, blending well. Pour batter into two greased and floured 8-inch round cake pans. Bake at 350 degrees for 30 minutes. Cool. Split each layer into two layers. Spread icing between each layer and on top.
Mix milk and flour; cook until mixture boils. Cool throughly. Beat butter and sugar until white; add vanilla. Blend in flour mixture.