Preheat oven to 350°F (175°C). Grease and flour three 9-inch round baking pans.
In a large mixing bowl, combine flour, cocoa powder, baking powder, baking soda, salt, and sugar.
Add eggs, buttermilk, oil, and vanilla extract. Beat on medium speed until well combined.
Stir in boiling water (batter will be thin). Pour batter into prepared pans.
Bake for 30-35 minutes or until a toothpick inserted into the center comes out clean. Cool in pans for 10 minutes, then remove to wire racks to cool completely.
For the frosting: In a saucepan, combine evaporated milk, sugar, egg yolks, butter, and vanilla. Cook over medium heat, stirring constantly, until thickened (about 12 minutes). Remove from heat and stir in coconut and pecans. Cool until thick enough to spread.
Spread frosting between layers and over top and sides of cake.
Notes:
For best results, use room temperature ingredients.