Preheat the oven to 350°F (175°C). Grease three 9-inch round cake pans and line the bottoms with parchment paper.

Melt the chopped German-style chocolate in the boiling water, stirring until smooth, then set it aside to cool slightly.

Whisk the flour, baking soda, and salt in a bowl.

In a separate large bowl, beat the butter and sugar until light and fluffy, about 3 minutes.

Beat in the egg yolks one at a time, then add the vanilla and melted chocolate mixture.

Alternately add the flour mixture and buttermilk, beginning and ending with the flour. Mix just until combined.

In a clean bowl, beat the egg whites with a hand mixer until stiff peaks form.

Gently fold the egg whites into the batter in three additions, taking care not to deflate them.

Divide the batter evenly among the prepared pans and bake for 26 to 30 minutes. Cool the cakes in the pans for 15 minutes before turning out onto racks to cool fully.

Whisk the evaporated milk, sugar, and egg yolks in a saucepan over medium heat. Cook, stirring constantly, for 10 to 12 minutes until thickened.

Remove from heat, stir in butter and vanilla until melted, then add coconut and pecans. Cool the filling to room temperature.

Spread a third of the filling between each layer of cake, finishing with the filling on top. Leave the sides bare for a classic look.