Preheat the oven to 350°F. Line 4 cups of a muffin tin with paper liners. Gather all ingredients.

Pour the milk into a small bowl. Add the vinegar and let sit while you prepare the rest of the ingredients.

Sift together the flour, cocoa powder, baking soda, and baking powder in a small bowl.

In another bowl, whisk together the oil, vanilla, and brown sugar.

Add the dry ingredients to the oil and brown sugar mixture in two batches, alternating with the milk mixture. Whisk until smooth, but try not to over-mix.

Divide the batter between the 4 muffin cups and bake for 15-18 minutes, or until a toothpick inserted comes out clean. Let cool on a wire rack.

Next, make the frosting: in a small saucepan, add the evaporated milk, sugar, egg yolk, and butter. Turn the heat to medium-low and cook while stirring until mixture starts to simmer around the edges of the pan. Lower the heat slightly, then continue to cook while stirring another 1 minute. It will thicken.

Turn off heat, and stir in the pecans and coconut flakes. Pour the mixture into a bowl, let cool to room temperature, then refrigerate until ready to serve the cupcakes.

To serve, frost the cupcakes with the chilled frosting. It will be considerably thicker after chilling.