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 buttermilk, vegetable oil, eggs, and vanilla to the flour mixture and mix until well combined. Gradually add boiling water, mixing until the batter is smooth.
Divide the batter evenly among the prepared cake 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 from pans and cool completely on wire racks.
For the frosting, combine evaporated milk, sugar, egg yolks, butter, and vanilla in a saucepan. 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 before spreading on the cake.
Spread frosting between layers and on top of the cake. Serve and enjoy!