Step 1: Preheat your oven to 350°F (175°C) and line a 12-cup muffin tin with paper liners.
Step 2: In a large bowl, whisk together the flour, sugar, cocoa powder, baking soda, and salt.
Step 3: In a separate medium bowl, whisk together the eggs, buttermilk, vegetable oil, and vanilla extract until well combined.
Step 4: Pour the wet ingredients into the dry ingredients and mix on low speed until just combined. Slowly add the hot water (or coffee) and mix until the batter is smooth. The batter will be thin.
Step 5: Divide the batter evenly among the 12 muffin cups, filling each about two-thirds full.
Step 6: Bake for 20-25 minutes, or until a wooden skewer inserted into the center of a cupcake comes out clean. Let the cupcakes cool in the muffin tin for a few minutes before transferring them to a wire rack to cool completely.
Step 7: While the cupcakes cool, prepare the frosting. In a medium saucepan, combine the evaporated milk, sugar, egg yolks, and butter. Cook over medium-low heat, stirring constantly, until the mixture thickens (about 10-12 minutes). It should be thick enough to coat the back of a spoon.
Step 8: Remove from heat and stir in the vanilla extract, shredded coconut, and chopped pecans. Mix well and let the frosting cool completely to room temperature. It will thicken further as it cools.
Step 9: Once the cupcakes are completely cool, spoon or pipe the coconut-pecan frosting generously onto each cupcake. Serve immediately or store as directed.