Pre-heat the oven to 180°C and prepare 2 x 8” round cake tins.
Pour the coconut milk, coconut rum, desiccated coconut and vanilla extract into a small saucepan and bring to the boil. Simmer for a couple of minutes, giving it a good stir, then turn off the heat and let sit for 30 minutes.
Cream the butter and sugar for a few minutes until light and fluffy.
Add the eggs in one at a time, don’t worry if the mixture looks a bit lumpy it will come together.
Sift the flours and baking powder together.
Add the flour alternately with the coconut mixture, adding the flour in three additions and the milk in two (begin and end with the flour), scrape down the sides of the bowls as needed and mix until just combined.
Divide the cake batter between the two sandwich tins and bake for around 18-20 minutes until the cake starts to brown and come away from the sides.
Meanwhile you can make the sugar syrup. Put all the ingredients in a small saucepan and bring to the boil. Simmer for around three minutes then turn off the heat.
When the cakes are ready, take them out of their tins after five mins resting. Poke the top of the cakes several times with a cocktail stick.
Brush the sugar syrup all over the two cakes, then leave them to cool before slicing in half horizontally to make four sponge layers.
Heat egg whites and caster sugar in a bain marie, stirring constantly until the sugar has dissolved and the temperature has reached 71°C.
Remove the egg whites and sugar from the heat and pour into a stand mixer with whisk attachment. Whisk until the mixture forms stiff peaks.
Change the attachment to a paddle attachment. On a low speed add the butter slowly cube by cube. When you have almost added all the butter the mixture will look curdled. Do not fret – this is supposed to happen and just means you are nearly done. Just continue to add all the butter. Once the butter is totally incorporated the frosting will miraculously become a smooth velvety consistency.
Add the salt, the vanilla extract and the melted chocolate. Mix until thoroughly combined.
After frosting the cake, decorate with the coconut flakes.