Begin by making the plain sponge cake:
1. Preheat the oven to 180°C/Gas Mark 4. Grease and base of a deep 23cm cake tin.
2. Whisk the oil, buttermilk, vinegar, eggs, sugar and vanilla together. In a separate bowl sift in the flour and baking powder, then add to the wet mix and fold in quickly.
3. Pour the mixture into the prepared cake tin. Bake for 25-30 minutes or until the cake is springy to the touch. Turn the cake out and leave to cool completely.
To make the coloured cake:
1. Grease and base line one 23cm loose bottom cake tin. Heat your oven to 180°C/Gas Mark 4.
2. Place the butter and sugar into a large mixing bowl. Use an electric whisk, beat until thoroughly blended. Add the eggs one at a time mixing well between each addition.
3. Add the mashed ube and ube extract and beat again until the mixture has turned a lovely shade of purple. Fold in the flour and baking powder until you have a smooth mixture, pour into the prepared tin.
4. Bake in the oven for 25 minutes or until the cake is firm to the touch and a skewer comes out clean when inserted into the middle.
5. Leave to cool in the tin for 5 minutes, then remove and leave to cool completely on a wire rack.
To make the frosting:
1. Beat the cream cheese, butter and vanilla together until smooth. Add the cooled white chocolate then gradually add the icing sugar. Beat until smooth.
2. Chill the icing for at least 1 hour or until set.
1. Take the cakes and cut each cake in half horizontally to make 4 discs. Put one coloured disc on the base of a cake stand, spread a little frosting over the top.
2. Next take a vanilla sponge disc and sit this on top of the coloured disc. Repeat with the other sponge discs alternating between the coloured and plain layers. Spread the remaining frosting all over the sides and top of the cake so it is completely covered.
3. Sprinkle the coconut over the top of the cake and press onto the sides until all the cake is completely covered in coconut.
Note: If you cant get hold of 'Ube' you could use squash or sweet pototo and add orange zest to and juice to the frosting. This will create a lovely orange layer instead of purple.