Pre heat your oven to 180°C and grease and line a round 9 inch loose bottomed cake tin.
Add the dairy free butter, brown sugar, cinnamon and lemon zest to a bowl and whisk well using an electric whisk until creamy.
Add the eggs 1 at a time and continue to whisk the mixture.
Stir in the self raising flour and xanthan gum to the mixture.
Peel and grate 2 of the apples. Fold the grated apple into the mixture along with your sultanas and then pour the mixure into your greased cake tin.
Peel and slice the remaining 2 apples. Press the sliced apples into the top of your cake.
Bake in the oven for around an hour and 15 minutes, or until a skewer comes out clean. You may need to cover the top with foil towards the end to prevent it from burning.
Leave to cool in the tin and enjoy.
Optional: Sift a little icing sugar over the top of the cake.