Cream shortening and sugar. Add eggs, beating well after each addition. Beat in food coloring and cocoa. Add buttermilk alternately with flour. Beat in salt and vanilla. Stir in vinegar and baking soda. Pour into two 8-inch round greased baking pans. Bake at 350F for 30-35 minutes, cool. Frost with icing.
For the icing: In a saucepan, stir flour into milk making a paste. Cook over low heat until thick stirring constantly. Remove from heat and set aside to cool. Beat butter and shortening until well mixed; beat in sugar. Mix in cooled paste. Stir in vanilla. (You can add chopped nuts, if desired.)
