Preheat the oven to 350°F (175°C).

Grease and flour two 9-inch round cake pans.

In a large mixing bowl, sift together flour, sugar, cocoa powder, baking soda, baking powder, and salt.

Add the buttermilk, vegetable oil, eggs, and vanilla extract to the dry ingredients and mix until just combined.

Carefully stir in the boiling water until the batter is smooth.

Divide the batter evenly between the prepared pans and bake for 30 minutes or until a toothpick inserted in the center comes out clean.

Remove the cakes from the oven and let them cool in the pans for 10 minutes, then transfer to a cooling rack to cool completely.

To make the frosting, in a saucepan combine sugar, milk, and egg yolks and cook over medium heat, stirring constantly, until thickened, about 5 minutes.

Remove the frosting from heat and stir in the coconut and pecans, then let it cool until spreadable.

Once the cakes are completely cooled, spread the frosting between the layers and over the top and sides of the cake.