Preheat oven to 350°F (175°C). Grease and flour three 9-inch round cake pans.
In a large 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 (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 frosting: In a medium saucepan, combine evaporated milk, sugar, egg yolks, butter, and vanilla. Cook over medium heat, stirring constantly, until thickened and golden brown, about 12 minutes. Remove from heat and stir in coconut and pecans. Cool to room temperature.
Spread frosting between layers and over top and sides of cake.