Preheat oven to 400°F and grease a 13x18 inch sheet pan.

In a large bowl, whisk together the flour, granulated sugar, and cocoa powder.

In a saucepan, combine the water, butter, shortening, and chopped chocolate. Cook over medium heat, stirring frequently, until melted and smooth.

Pour the chocolate mixture into the dry ingredients and whisk until fully incorporated.

Whisk in the buttermilk, baking soda, salt, eggs, and vanilla until you have a smooth batter.

Pour batter into the prepared sheet pan and spread it out evenly.

Bake for 20-22 minutes until a toothpick inserted in the center comes out clean. Allow to cool completely.

For the frosting: In a saucepan, whisk together the evaporated milk, egg yolks, butter, and both sugars. Bring to a simmer over medium heat, stirring frequently.

Once simmering, continue cooking for 10-12 minutes, stirring constantly, until thickened to a spoonable consistency.

Remove from heat and stir in the coconut, pecans, and vanilla.

Let frosting cool slightly for 5-10 minutes until no longer piping hot.

Pour frosting over the cooled cake and use an offset spatula to spread it evenly.

Refrigerate the frosted cake for 1-2 hours before slicing and serving.