Preheat your oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.

In a large bowl, cream together 1 cup softened butter and 2 cups sugar until light and fluffy.

Beat in the 4 egg yolks one at a time, mixing well after each addition. Stir in the vanilla extract.

In a separate bowl, whisk together the cocoa powder, flour, baking soda, and salt.

Add the dry ingredients alternately with the buttermilk to the butter mixture, beginning and ending with the dry ingredients. Mix until just combined.

Stir in the hot water until the batter is smooth.

In a clean bowl, beat the 4 egg whites until stiff peaks form. Gently fold the egg whites into the chocolate batter.

Pour the batter evenly into the prepared cake pans. Bake for 30 to 35 minutes, or until a wooden pick inserted into the center comes out clean. Let cakes cool in pans for 10 minutes before inverting onto a wire rack to cool completely.

Prepare the frosting: In a medium saucepan, combine ½ cup butter, sweetened condensed milk, and 2 egg yolks. Cook over medium-low heat, stirring constantly, until the mixture thickens enough to coat the back of a spoon (about 8 to 10 minutes). Do not boil.

Remove the saucepan from the heat. Stir in the chopped pecans and flaked coconut. Let the frosting cool slightly until it is thick but still spreadable.

Place one cooled cake layer on a serving plate. Spread about half of the coconut pecan frosting evenly over the top. Place the second cake layer on top.

Frost the top and sides of the entire cake with the remaining frosting.