Preheat your oven to 350°F (175°C). Grease and flour three 9-inch round cake pans to prevent sticking.

In a large bowl, combine the flour, baking soda, and salt.

In a separate bowl, mix the cocoa powder, granulated sugar, brown sugar, and softened butter until creamy using an electric mixer.

Beat in the egg yolks, one at a time, followed by the vanilla extract.

Alternate adding the buttermilk and the flour mixture to the cocoa mixture, starting and ending with the flour. Mix until just combined.

Carefully stir in the boiling water until the batter is smooth.

In a separate bowl, beat the egg whites until stiff peaks form. Gently fold them into the batter.

Divide the batter evenly among the prepared pans and bake for 25-30 minutes.

The cakes are done when a toothpick inserted into the center comes out clean.

While the cakes cool, prepare the coconut-pecan filling by combining sugar, evaporated milk, butter, and egg yolks in a saucepan over medium heat.

Stir continuously until it thickens, about 12-15 minutes. Remove from heat; stir in vanilla, coconut, and pecans. Let it cool completely.

For the chocolate frosting, beat the softened butter and cocoa powder in a bowl.

Gradually add powdered sugar and milk, mixing until creamy. Add vanilla extract; mix well.

Once the cakes are cooled, place one layer on a serving plate. Spread a layer of coconut-pecan filling on top, then add the second cake layer.

Repeat. Place the last layer on top and frost the top and sides with chocolate frosting.

Decorate the top with any remaining coconut and pecans for a beautiful presentation.