Preheat oven to 350°F (175°C).

Grease two 9-inch round cake pans and line with parchment paper.

In a large bowl, whisk together flour, baking powder, baking soda, salt, and cocoa powder.

In another bowl, mix granulated sugar, brown sugar, buttermilk, vegetable oil, eggs, and vanilla extract until well combined.

Gradually add wet ingredients to dry ingredients, mixing until combined. Stir in boiling water (the batter will be thin).

Divide the batter evenly between the prepared pans and bake for 25-30 minutes, or until a toothpick comes out clean.

Allow the cakes to cool in the pans for 10 minutes, then turn onto a wire rack to cool completely.

In a saucepan over medium heat, cook sugar, evaporated milk, butter, and egg yolks, stirring constantly until it thickens.

Remove from heat and stir in vanilla, coconut, and pecans. Allow to cool slightly.

Once cakes are cooled, place one layer on a serving plate and spread frosting on top.

Place the second layer on top and frost the top and sides of the cake.