Preheat your oven to 350°F (175°C) and prepare the cake pans.
In a large mixing bowl, combine the dry ingredients: flour, sugar, cocoa powder, baking powder, baking soda, and salt.
In another bowl, mix the wet ingredients: buttermilk, oil, eggs, and vanilla.
Pour the wet ingredients into the dry ingredients and mix until just combined.
Carefully stir in the boiling water until the mixture is smooth.
Divide the batter evenly between the prepared cake pans and bake for 30-35 minutes.
Allow the cakes to cool in the pans for about 10 minutes, then transfer them to a wire rack.
While the cakes cool, prepare the coconut-pecan frosting.
Combine sugar, evaporated milk, butter, and egg yolks in a saucepan and cook over medium heat, stirring continuously.
Once the mixture thickens, remove from heat and stir in coconut and pecans.
Spread the cooled frosting between the cake layers and on top of the cake.
Allow the cake to set for at least 30 minutes before serving.
