Preheat the oven to 180c and line two 20cm cake tins with baking parchment. Set aside.
Place the psyllium husks into a spice grinder or high speed blender and blitz until powdered. Transfer to a small bowl and whisk together with 2 tbsp water. Set aside to thicken.
In a medium bowl, whisk together the flour, desiccated coconut, baking soda and salt. Set aside.
In the bowl of a stand mixer fitted with the paddle attachment, beat together the melted coconut oil, sugar, coconut milk, vinegar, coconut extract and psyllium husk mixture until smooth. The psyllium husk mixture tends to clump together so be sure to beat on a high speed until very smooth.
To the stand mixer, add the flour mixture and beat until combined. Do not over beat.
Divide the cake batter between the two prepared cake tins and place in the oven for 25-30 minutes. Once baked, a skewer inserted into the centre should come out clean.
Remove the baked cakes from the oven and place on a cooling rack until cool enough to handle. Remove from the baking tins and allow to cool completely.
While the cakes are cooling, make the buttercream frosting.