Preheat oven to 350º F (180º C).
Butter the inside of a pie dish, or similar sized baking dish.
Place the sliced apples in a large bowl and add the lemon juice, lemon rind, and sugar, and toss to mix evenly. Put the apples into the greased pie dish and set aside.
Sift the flour and baking powder into a bowl so that they are evenly mixed.
Cream the sugar and butter (for the topping) until light and fluffy, then beat in the egg.
Gently fold in the flour and baking powder, until well combined, without over mixing.
Spread the mixture evenly over the apples. It's fine if it doesn't cover all the fruit, and it will be more like a thick mixture than a runny batter.
Bake for 40 to 45 minutes or until the sponge is firm and golden brown.
Enjoy with custard, preferably, or fresh cream.
