Preheat oven to 350 degrees. Stir together cocoa and boiling water in small bowl until smooth; set aside. Cream shortening, sugar and vanilla in large mixer bowl until light and fluffy. Add eggs; beat well. Combine flour, baking soda and salt; add alternately with buttermilk to creamed mixture. Blend in cocoa mixture. Pour into three greased and floured 8" or two 9" layer pans. Bake for 25-30 minutes for 8" pans or 35-40 minutes for 9" pans, or until cake tester comes out clean. Cool 10 minutes; remove from pans. Cool completely; frost as desired.