Preheat oven to 350°F (175°C). Grease and flour three 8-inch or two 9-inch round cake pans.

1. In a large bowl, whisk together flour, sugar, cocoa powder, baking soda, baking powder, and salt.
2. Add eggs, buttermilk, oil, and vanilla. Beat until smooth and well combined.
3. Stir in boiling water or hot coffee until the batter is thin and smooth.
4. Divide the batter evenly between the prepared pans.
5. Bake for 28–32 minutes, or until a toothpick inserted in the center comes out clean.
6. Let cakes cool in the pans for 10 minutes, then transfer to wire racks to cool completely.
7. Meanwhile, in a saucepan over medium heat, combine evaporated milk, egg yolks, granulated sugar, brown sugar, and butter.
8. Cook, stirring constantly, for 10–12 minutes until thickened and bubbly.
9. Remove from heat and stir in vanilla, coconut, and pecans. Let cool completely.
10. Place one cake layer on a serving plate and spread with frosting. Repeat with remaining layers, frosting only the tops.
11. Optionally frost sides with chocolate buttercream or leave them unfrosted.
12. Chill the cake for 30 minutes before slicing for cleaner cuts.