Preheat the oven to 220C/425F/Gas 7.
For the caramelised apple, melt the butter in an ovenproof frying pan and add the chopped apple. Stir well, then sprinkle over the sugar and cook for 2-3 minutes, until lightly caramelised.
Meanwhile, for the batter, place all the batter ingredients into a food processor and blend to form a smooth batter.
Spoon the batter over the caramelised apples in the pan. Transfer to the oven and bake for 12-15 minutes, until well risen and golden-brown.
Dust generously with icing sugar. Serve hot with a jug of cream on the side.