Chocolate cake

1. This recipe requires 4 mixing bowls. Use the biggest one for the egg yolks.
2. Cook the sweet potato (microwave for 10 minutes on high) until soft, then mash and set aside.
3. Preheat the oven to 180 degrees Celsius.
4. Lightly grease 2 cake pans (20 cm diameter x 4 cm depth) with non-stick spray.
5. Add the bicarbonate of soda to the warm, mashed sweet potato, stir in lightly and leave to foam.
6. Sift the cocoa powder into a large bowl. Pour the oil and water over the cocoa and mix well. Add the sweet potato, apple, buttermilk or yoghurt, and the vanilla essence. Set aside.
7. Sift the flour, salt and baking powder into another bowl. Add the oat brand and stir, lifting the mixture up a few times with a spoon to incorporate air.
8. Beat the egg yolks until frothy in the largest mixing bowl, using an electric beater. Add the Castor sugar (or sugar substitute) in 2 batches, beating for 1 minute after each addition.
9. Add the dry ingredients to the egg and sugar mixture, alternately with the buttermilk/yoghurt and apple mixture.
10. Whisk the egg whites to the soft-peak stage in another bowl and fold lightly into the batter.
11. Spoon the batter into the cake pans and spread it out to the sides, so that the cake does not rise too high in the centre.
12. Bake for 30-40 minutes, until done. Remove from the oven and leave to cool before removing the cake from the cake pan. Loosen the sides with a knife before removing the cake.
13. Icing: sift the icing sugar and cocoa powder into the cottage cheese. Mix gently.
14. Spread some icing on the top of 1 cake layer, then place the other layer on top. Use the rest of the icing to cover the top of the cake generously.