Preheat your oven to 350°F (175°C) and grease and flour a 13×18 inch baking sheet.

In a large mixing bowl, whisk together the flour, granulated sugar, cocoa powder, baking soda, baking powder, and salt until well combined.

In another bowl, combine the melted butter, buttermilk, eggs, and vanilla extract, mixing until well combined.

Gradually add the wet ingredients to the dry ingredients, mixing gently until just combined.

Carefully stir in the boiling water until the batter is smooth and glossy.

Pour the batter into the prepared baking sheet and spread evenly.

Bake for 20-25 minutes or until a toothpick inserted into the center comes out clean.

Allow the cake to cool completely in the pan.

In a saucepan over medium heat, combine sweetened condensed milk, brown sugar, butter, vanilla extract, egg yolks, and salt.

Stir continuously for 8-10 minutes until thickened.

Remove from heat and fold in the shredded coconut and chopped pecans.

Once the cake is completely cooled, spread the coconut-pecan topping evenly over the cake.

Allow the topping to set for a few minutes before slicing into squares.