To make the cake, preheat oven to 350F. Grease a 9x13-inch metal baking pan. Set aside.
In a large, heat-proof bowl, add chopped chocolate.
4 ounces German sweet chocolate
Pour the boiling water over the chocolate, and let it stand for 5 minutes.
1 cup boiling water
Stir until chocolate has melted and is combined with the water.
Add the oil, buttermilk, and sugar. Whisk until well-combined.
½ cup oil, ½ cup buttermilk, 1 ¾ cups granulated sugar
Whisk in the eggs and vanilla until well-combined.
4 large eggs, 1 teaspoon vanilla extract
Add the flour, cocoa powder, baking powder, baking soda, and salt. Stir in just until combined. Don't overmix.
2 ¼ cups all-purpose flour, 2 tablespoons cocoa powder, 1 teaspoon baking powder, ½ teaspoon baking soda, ¼ teaspoon salt
Pour the batter into the prepared baking pan.
Bake for 25-35 minutes, or until a wooden toothpick inserted in the center comes out clean.
Cool to room temperature.
To make the topping, add the egg yolks, milk, and brown sugar to a large saucepan.
3 egg yolks, 1 cup evaporated milk, 1 ½ cups brown sugar
Whisk until combined.
Add butter.
¼ cup butter
Heat saucepan over low heat.
Cook for 10 minutes, whisking regularly, until mixture has thickened.
Remove from heat.
Whisk in vanilla extract.
1 teaspoon vanilla extract
Add coconut and pecans, and stir in.
2 ½ cups sweetened shredded coconut, 1 ½ cups chopped pecans
Let topping cool for 15 minutes.
Spread topping over cake, and let cool to room temperature before serving.
Video
Notes
German chocolate: I like to use Baker's German sweet chocolate.
Oil: I've used vegetable oil and melted coconut oil in this cake. If you use melted coconut oil, the buttermilk and eggs should be at room temperature so that the oil doesn't solidify.
Buttermilk: Regular or low-fat will work. If you don't have buttermilk, you can make a substitute with this buttermilk substitute recipe.