Preheat the oven to 180°C. Grease two 20-cm round cake tins and line the bases with baking paper.
Mix the cocoa powder with the hot water into a smooth paste.
In a large mixing bowl, add all the cake ingredients, then the cocoa mixture. Using an electric mixer or wooden spoon, stir until smooth.
Divide the batter into the two tins evenly
Bake the cakes for about 25-30 minutes. Insert a skewer, if it comes out clean, the cakes are done.
Turn off the oven but leave the cakes in their tins in there. Open the door and let them cool down gently for 5 minutes.
Turn out the cakes on a wire rack, let them cool completely
In the meantime: mix all the buttercream ingredients in a bowl. Add enough shredded coconut to create a thick, spreadable cream.
Spread some of the buttercream on top of one of the cakes. Put the other cake on top, press down.
Cover the cake completely with the spread. Sprinkle more shredded coconut on top and/or any edible decoration you'd like to use to mark your occasion.
Put the cake in the fridge for a couple of hours for the buttercream to set.