• Gather all ingredients. Preheat the oven to 350°F (175°C) and grease a 9x13-inch metal baking pan; set aside.

For Cake:

• Place the chopped German sweet chocolate in a large heatproof bowl. Pour the boiling water over it, let sit about 5 minutes, then stir until the chocolate melts and the mixture is smooth.
• Whisk the oil, buttermilk, and granulated sugar into the melted chocolate until combined and glossy.
• Beat in the eggs and vanilla until evenly incorporated.
• In a separate bowl, combine the flour, cocoa powder, baking powder, baking soda, and salt; then fold these dry ingredients into the wet mixture just until blended—avoid overmixing.
• Spread the batter in the prepared pan and smooth the top.
• Bake for 25 to 35 minutes, or until a toothpick inserted into the center comes out clean. Remove from oven and allow the cake to cool to room temperature.

For Topping:

• In a large saucepan, whisk together the egg yolks, evaporated milk, and packed brown sugar until smooth.
• Add the butter and place the pan over low heat. Cook, whisking frequently, until the mixture thickens, about 10 minutes.
• Remove the pan from heat, stir in the vanilla, then fold in the shredded coconut and chopped pecans. Let the topping cool roughly 15 minutes so it thickens slightly.
• Spread the warm topping evenly over the cooled cake. Allow the cake to come to room temperature and the topping to set before slicing and serving.