Heat oven to 350 degrees. Grease and flour two 9-inch round baking pans.
Combine together cocoa and water in small bowl until smooth; set aside.
In a large bowl of a stand mixer beat butter, sugar and vanilla in large bowl until light and fluffy. Add eggs, one at a time, beating well after each addition.
In a medium bowl, combine together the flour, baking soda and salt.
To the butter mixture add by alternating between the dry ingredients, the chocolate mixture, and buttermilk beating just enough to blend each time. Pour batter into prepared pans.
Bake 25 to 30 minutes or until top springs back when touched lightly or cake tester comes out clean. Cool 5 minutes; remove from pans to wire racks. Cool completely.
Prepare the coconut-pecan frosting (recipe below) and frost cakes.
*TIP: To sour milk: Use 1 tablespoon white vinegar plus milk to equal 1 cup.