Preheat oven to 350°F. Line three 8" round baking pans with parchment paper, set aside.
Stir together cocoa and water in small bowl until smooth, set aside. Beat together your butter, shortening, sugar, salt and vanilla in large bowl until well combined.
Add eggs mixing well.
Stir 1-1/2 teaspoons baking soda into 1 cup buttermilk and add to butter mixture alternately with flour.
(ORANGE CAKE) Measure 1 2/3 cups batter into a small bowl and stir in remaining 1/8 teaspoon baking soda and 3 tablespoons buttermilk, orange peel, and orange extract.
Pour into one of your prepared pans.
(CHOCOLATE CAKE) Stir cocoa mixture into remaining batter and divide evenly between remaining pans.
Bake 25 to 30 minutes or until toothpick inserted in center comes out clean.
Cool 10 minutes; remove from pans to wire racks to cool completely.