Heat the oven to 350°F (175°C). Lightly grease a 9x13-inch metal baking pan and set it aside.

Place the chopped German sweet chocolate in a large heatproof bowl.

Pour the boiling water over the chocolate and let it rest for about 5 minutes so the chocolate softens.

Stir the chocolate and water together until the mixture is smooth and fully melted.

Whisk in the oil, buttermilk, and granulated sugar until the batter is even and smooth.

Add the eggs and vanilla, beating until they are incorporated into the batter.

Sift or add the flour, cocoa powder, baking powder, baking soda, and salt. Stir just until combined—avoid overmixing.

Pour the batter into the prepared pan and smooth the top.

Bake for 25 to 35 minutes, or until a toothpick inserted in the center comes out clean or with a few moist crumbs.

Remove the cake from the oven and allow it to cool to room temperature before adding the topping.

In a large saucepan, combine the egg yolks, evaporated milk, and packed brown sugar. Whisk until the mixture is smooth.

Add the butter to the saucepan and place it over low heat.

Cook gently over low heat, whisking frequently, for about 10 minutes until the mixture thickens and becomes creamy.

Remove the pan from the heat and stir in the vanilla extract.

Fold in the shredded coconut and chopped pecans until they are evenly distributed throughout the topping.

Let the topping cool for about 15 minutes so it thickens slightly and is easier to spread.

Spread the warm topping over the cooled cake, then allow the assembled cake to come to room temperature before slicing and serving.