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

In a large bowl, whisk together the flour, sugar, baking soda, and salt.

In a separate bowl, combine the buttermilk, oil, and 2 eggs. Add this wet mixture to the dry ingredients and mix until just combined.

In a small saucepan, combine the hot water and cocoa powder. Stir until the cocoa is dissolved. Pour this chocolate liquid into the cake batter and mix until smooth.

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

In a medium saucepan, melt the butter over medium heat. Stir in the evaporated milk and sugar. Cook, stirring constantly, until the mixture thickens slightly, about 5 minutes.

Remove the pan from the heat. Whisk in the 4 egg yolks one at a time, mixing well after each addition. Return the pan to low heat and cook, stirring constantly, for 2 minutes, being careful not to scramble the eggs. Do not boil.

Remove from heat and stir in the vanilla extract, pecans, and coconut. Let the frosting cool until it is thick enough to spread.

Assemble the cake by spreading a layer of frosting between the two cooled cake layers and covering the top and sides of the cake with the remaining frosting.