Preheat the oven to 180°C and grease a round ceramic 8 inch baking dish.
In a large saucepan, combine the apples and 100g of the caster sugar and add a little water. Bring to a simmer and cook gently for 2-3 minutes, making sure the sugar is dissolved. Strain the apples and discard the cooking liquor.
In a large mixing bowl, combine the remaining caster sugar with the rest of the ingredients and beat using an electric hand-held whisk for 4-5 minutes until smooth. Fold the apples in until incorporated. Spoon into the baking dish and bake for 50-60 minutes until a cake tester comes out clean when inserted into the centre of the cake.
Remove and allow to cool in the dish a little before serving and garnishing with a slice of apple.