Cream shortening, sugar and eggs. Make a paste of food coloring and cocoa. Add to creamed mixture. Add buttermilk alternating with flour and salt. Add vanilla. Add soda to vinegar (foams!!!), and blend in. Pour into 3 or 4 greased and floured 20 cm cake pans. Bake at 180ºC . for 24-30 minutes. Split layers fill and frost with the following frosting. Frosting: Add milk to flour slowly, avoiding lumps. Cook flour and milk until very thick, stirring constantly. COOL IT COMPLETELY!! Cream sugar, butter and vanilla until fluffy. Add to cooked mixture. Beat, high speed, until very fluffy. Looks and tastes like whipped cream.