Peel, core and thickly slice the apples.

Place the apples into a large saucepan, together with the lemon juice, vanilla sugar and water.

Cook over medium heat until the apples have softened but still retain their shape.

There should still be some liquid in the pan. If not, add a splash or two of water so that the fruit filling is more on the wet side than dry.

Taste the apples to see if you need to add more sugar, or maybe even more lemon juice. Apples vary in sweetness (and lemons vary in sourness), so you may need to adjust to taste.

Pour the cooked apples into a baking dish, about 23 cm/9 inches in diameter.

Preheat the oven to 180°C/360°F (without fan).

Beat the butter and sugar together until pale and fluffy.

Add the vanilla extract.

Beat in one egg at a time, followed by a tablespoon of the flour to prevent the batter from curdling.

Add the remaining flour and baking powder, as well as the milk.

Beat everything together until you have a thick and smooth batter.

Dollop the batter on top of the apples in the baking dish.

Use a spatula or palette knife to evenly spread the batter. Don't worry about stretching the batter to completely cover the apples - the batter will spread as it bakes in the oven.

Sprinkle the batter generously with demerera sugar.

Bake the pudding on the middle shelf of the oven for 30-40 minutes, or until the pudding is lightly golden and set in the centre.

Check the pudding at about 25 minutes to make sure it is not browning too quickly. If necessary, loosely cover it with a piece of foil.

Serve warm with vanilla ice-cream or custard.