Preheat the oven to 180°C/Gas Mark 4.
Wash and cut the apples into cubes, removing the peel. Roll out the apples with lemon juice and set aside.
Mix the flours with the baking powder and cinnamon.
In a bowl, beat the egg with sugar, milk and oil. Pour the dry ingredients into the liquid bowl and mix. Add the apples.
Pour the mixture into a cake tin lined with parchment paper, then add a sprinkling of demerara sugar.
Bake for 30 minutes.