Preheat oven to 170°C. Grease and line a 23cm round cake tin

Cut the small peeled apples into 1cm pieces. Place in a microwave bowl and add a little water. Microwave on high for 1 minute. Drain and set aside to cool.

Beat egg whites using a whisk beater until soft peaks form. Gradually add castor sugar and beat well until sugar is dissolved. Add egg yolks, orange zest and milk. Mix well. Fold in flour alternatively with melted butter and mix well. Stir in cooled diced apple.

Pour mixture into greased cake pan. Slice cored cooking apple finely and arrange on top of the cake batter, slightly overlapping the large pieces for the edge and using smaller pieces for the center. Combine extra sugar and cinnamon then sprinkle over the apple slices on top of the cake. Bake in the center of a moderate oven for 55 -60 minutes. Test to see if it is done by inserting a clean metal skewer into the center of the cake, when it comes out clean the cake is done.