Preheat oven to 350°F (175°C). Grease and flour three 9-inch round cake pans.
In a large mixing bowl, combine flour, sugar, brown sugar, cocoa powder, baking powder, baking soda, and salt.
Add eggs, buttermilk, oil, and vanilla. Beat on medium speed until smooth. Stir in boiling water until well combined.
Pour batter evenly into prepared pans. Bake for 30-35 minutes or until a toothpick inserted in the center comes out clean.
Cool in pans for 10 minutes, then remove to wire racks to cool completely.
For frosting, combine evaporated milk, sugar, egg yolks, butter, and vanilla in a saucepan. 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.