Sift the flour and salt together in a bowl, make a well in the centre and stir in the egg, then gradually add half the milk and water, beating well until the batter is creamy.
Add the remaining liquid and whisk the batter until smooth and light. Stand in a cool place for 20 minutes.
Set oven to 425ºF or Mark 7.
Place the apples in melted butter in a heavy frying pan and add the lemon peel, juice, cinnamon and sugar. Cook gently until the apples are just soft.
Put the lard in a 7 1/2 - 8 inch square roasting tin and heat at the top of the oven until smoking.
Very carefully arrange the apple mixture in the hot fat, then pour the batter over.
Bake for 20 minutes, then reduce the temperature to 375ºF or Mark 5 and bake a further 20 minutes until the batter is firm and golden; because of the apple mixture, it will not rise as much as a plain batter.