Preheat your oven to 350°F (175°C) and grease three 9-inch round cake pans.
In a large bowl, combine flour, sugar, cocoa powder, baking soda, baking powder, and salt.
Add buttermilk, vegetable oil, eggs, and vanilla to the dry ingredients and mix well.
Slowly pour in boiling water and mix until smooth.
Divide the batter evenly among the prepared pans.
Bake for 30-35 minutes or until a toothpick inserted comes out clean.
Let the cakes cool in the pans for 10 minutes, then transfer to wire racks.
For the frosting, combine evaporated milk, sugar, and butter in a saucepan over medium heat.
Stir constantly until the mixture thickens (about 10-12 minutes).
Remove from heat and stir in egg yolks, coconut, pecans, and vanilla.
Spread frosting between the layers and on top of the cake once completely cool.