Your guests will be so impressed by this cake! Alternating layers of cocoa and orange cake in between orange buttercream make this recipe truly special. And like good friends, the different flavors bring out the best in each other.
Heat oven to 350°F. Grease three 8- or 9-inch round baking pans; line with wax paper.
Stir together cocoa and water in small bowl until smooth; set aside. Beat butter, shortening, sugar, salt and vanilla in large bowl until well blended. Add eggs; beat well. Stir 1-1/2 teaspoons baking soda into 1 cup buttermilk; add to butter mixture alternately with flour.
Measure 1-2/3 cups batter into small bowl; stir in remaining 1/8 teaspoon baking soda and 3 tablespoons buttermilk, orange peel and orange extract. Pour into one prepared pan. Stir cocoa mixture into batter; divide evenly between remaining two prepared pans.
To sour milk: Use 1 tablespoon white vinegar plus milk to equal 1 cup; use 1/2 teaspoon white vinegar plus milk to equal 3 tablespoons.
Bake 25 to 30 minutes or until wooden pick inserted in center comes out clean. Cool 10 minutes; remove from pans to wire racks. Carefully peel off wax paper. Cool completely.
Beat butter, 1 cup powdered sugar, orange peel and vanilla in large bowl until creamy. Add remaining powdered sugar alternately with milk, beating to spreading consistency. If necessary, add additional milk, 1/2 teaspoon at a time, to get desired spreading consistency. About 3 cups frosting.
*The % Daily Value tells you how much a nutrient in a serving of food contributes to a daily diet 2,000 calories a day is used for general nutritional advice.