Prepare a 8x8 inch baking pan by lining it with parchment paper. Set aside. Preheat oven to 350 degrees.
For the Bottom:
Vigorously stir together the melted butter, brown sugar, vanilla extract, and egg until well mixed.
Add flour and cocoa powder. Stir into the wet ingredients until well combined.
Pour into prepared baking sheet. Press batter into corners and along the sides of the pan. Try to get the bottom layer as flat and as evenly distributed as possible.
For the Middle:
Stir the vanilla extract into the sweetened condensed milk until combined.
Add the coconut and stir until completely incorporated.
Spoon this mixture over the bottom layer. Try to avoid too much movement; this will help to keep the dark layer and the light layer separated, which will make the square look much prettier. I like to use a tablespoon to scoop up the coconut mixture and dot the top of the chocolate layer. When done, very gently spread the coconut layer evenly and flat using an off-set spatula.
Bake for 30 minutes. Remove from oven and allow to cool completely. Do not remove from baking pan.
For the Top:
Whisk together all ingredients until well combined. Evenly spread over the cooled squares with an off-set spatula.
Allow to squares to set up in the fridge for one hour. Remove from pan using the parchment paper to help lift. Cut into 16 squares. (You can cut the squares smaller if you prefer.)