1.Preheat oven to 190°C. Grease 12-hole (⅓-cup/80ml) muffin pan, or line with paper patty cases.
2.Combine butter, flours, cinnamon, caster sugar, egg and milk in large bowl; stir until just combined.
3.Divide half the mixture among holes of prepared pan; make well in centre of each muffin, drop 1 level teaspoon of custard and 2 level teaspoons of apple into each well. Top with remaining muffin mixture; sprinkle with combined brown sugar and extra cinnamon.
4.Bake muffins about 25 minutes. Stand muffins in pan for a few minutes before turning onto wire rack.