Adjust oven rack to middle position and heat oven to 350°F.
Spray two 8-inch by 2-inch cake pans with Bakers’ Spray. If desired, line the bottom of the pans with parchment paper.
Chop the chocolate into thin slivers.
Bring water to a boil, remove from heat and add chocolate, stirring to melt; cool completely.
In the bowl of an electric mixer, whisk the egg whites until stiff peaks form. Carefully, transfer the whipped egg whites to a different bowl; set aside. Save the 4 eggs yolks for the frosting.
While the chocolate cools, place butter and sugar in the same bowl (no need to wash) and beat until butter is lighter in color and the mixture is smooth and fluffy(er).
Beat in egg yolks, one-at-a-time.
Add chocolate water and vanilla; stir to incorporate completely.
In a medium bowl, whisk together flour, baking soda and salt.
In a separate bowl, whisk together the buttermilk and sour cream.
With mixer on low speed, alternately add flour mixture and buttermilk/sour cream mixture (beginning and ending with the flour mixture). Mix just until incorporated after each addition.
Use a rubber spatula to fold the beaten egg whites into the cake batter, and pour the batter into the prepared cake pans.
Bake at 350°F for 25-35 minutes or until a toothpick inserted in the middle of each cake layer comes out clean.
Remove from oven and cool on a wire rack 15 minutes. Remove cakes from pan and cool completely on the cooling rack.
To make a 4-layer cake, cut each cake layer into two layers, horizontally.
Prepare Coconut Pecan Frosting and spread between each layer and on the top of the cake.