Pre-heat your oven to 160C Fan/180C/350F/Gas Mark 4, and grease and line three 8" cake tins (that are at least 2" deep)
Melt the coconut oil and creamed coconut blocks in a pan on a low heat
Remove from the heat and pour into a mixing bowl, add the caster sugar and mix well, leave to cool for 10 minutes
Add the eggs and whisk until fully incorporated
Add the self raising flour and whisk in until you can't see any flour anymore
Mix in the dessicated coconut
Divide the mixture between the tins, use scales for accuracy
Bake them for 30-35 minutes or until a skewer inserted in the middle comes out clean. Leave them to fully cool either in the tins or remove from the tin and place on cooling racks
To make the buttercream mix the butter and icing sugar together. Once it starts to come together add the coconut flavouring and mix until smooth. I use my electric hand whisk to do this but you can also do it by hand with a spoon. If the buttercream is too stiff then you can add some milk to it
If the cakes have domed on top, level them off with a cake leveller or a serrated knife
Put one of the sponges on a decorating turntable and spread over some buttercream, add the second sponge and spread over more buttercream, then add the third sponge
Fully crumb coat the cake, this means cover the whole cake in a thin layer of buttercream to seal in the cake crumbs, then put it in the fridge for 30 minutes to firm up
Put two heaped tablespoons of buttercream into a bowl and colour with the blue food colouring to a light blue shade, do the same with two more heaped tablespoons of buttercream in another bowl and colour it a slightly darker blue (or lighter if you've gone too dark with the first batch)
Cover the whole cake in a layer of the white buttercream then add blobs of the two blue buttercreams randomly all around the sides
Use a cake scraper to smooth the sides and create the watercolour effect, making sure to wipe off excess buttercream from the scraper as you go. Once the sides are smoothed to your liking, add some blue buttercream to the top of the cake and smooth it out using a palette
knife
Transfer the cake to your cake stand or serving plate
Add the digestive biscuit on top and around the sides
Add your chocolate shells and any other decoration you are using
Leftovers will keep in an airtight container in a cool place for 2-3 days