Combine batter, shortening, cocoa and water in a small saucepan. Bring to a boil, stirring frequently. Remove from heat. In a large bowl, combine flour and sugar. Stir in slightly cooled chocolate mixture. Stir eggs into buttermilk. Add soda and vanilla to buttermilk. Stir buttermilk mixture into batter. Pour batter into a 9x13-inch greased baking pan. Bake at 400 degrees for 25 minutes. Frost with caramel frosting.