Cream shortening, sugar and vanilla; add eggs, one at a time. Make a paste of the cocoa and food coloring, add the mixture above. Add salt. Add sifted flour alternatively with buttermilk. Add vinegar and baking soda (it’ll fizz); mix.
Pour batter into well-greased and floured bundt pan. Bake at 350 for about 35 minutes. Cool 10 minutes and remove from pan. Allow to cool completely, then ice.
Cook flour and milk until thick, stirring constantly; allow to cool completely. Beat sugar, butter and vanilla to a cream. Combine and frost.