Make the Cupcakes:

1. Preheat Oven: Preheat your oven to 350°F (175°C) and line a 12-cup muffin tin with cupcake liners.
2. Mix Dry Ingredients: In a medium bowl, sift together the flour, cocoa powder, baking powder, baking soda, and salt. Set aside.
3. Cream Butter and Sugar: In a large bowl, beat the butter and sugar together until light and fluffy. Add the eggs one at a time, then stir in the vanilla extract.
4. Combine Wet and Dry Ingredients: Gradually add the dry ingredients to the butter mixture, alternating with the buttermilk, beginning and ending with the dry ingredients. Stir in the hot water until the batter is smooth.
5. Bake: Divide the batter evenly among the cupcake liners. Bake for 18-20 minutes, or until a toothpick inserted into the center comes out clean. Let cool completely before frosting.

Make the Coconut-Pecan Frosting:

1. Cook the Mixture: In a medium saucepan, combine the butter, evaporated milk, sugar, and egg yolks. Cook over medium heat, stirring constantly, until the mixture thickens (about 8-10 minutes).
2. Add Coconut and Pecans: Remove from heat and stir in the vanilla extract, shredded coconut, and chopped pecans. Let the frosting cool to room temperature.

Assemble the Cupcakes:

1. Spread the coconut-pecan frosting over the top of each cooled cupcake.
2. Drizzle with melted chocolate or sprinkle with toasted coconut flakes if desired.