I don't have a skillet that can go in the oven so I prepared the apples in a saucepan and then made the pandowdy in a tin.
Melt the butter in a saucepan then add the apples, sugar, lemon zest and cinnamon and cook over low heat until the apple begins to caramelise. When this happens, remove the apples from the heat.
To make the pastry, pour the flour and salt into the bowl of an electric mixer. Attach the paddle then add the very cold butter and using a teaspoon drop in little blobs of the cold shortening and mix it on the slow setting to cut the fat into the flour. This can be done by hand if you don't have an electric mixer.
Keep the motor running slowly and add the milk a little at a time until the dough comes away from the sides of the bowl.
Tip the dough out onto a floured surface and form it into a bowl with your hands.
Pre-heat the oven to 200C(392F) fan-forced.
Place the fruit into the tin you are using.
Roll out the dough until it is roughly the size of the tin. It's quite a thick dough.
Place the dough over the tin and tuck in the edges. Nigella says that it's meant to look rather 'ramshackled' so don't worry if it looks messy.
Make 3 slashes across the top of the pastry and sprinkle it with a little bit of caster sugar.
Bake the pandowdy for about 25 minutes or until the pastry turns golden.
I served it with ice cream.
You can prepare the pandowdy ahead of time but make sure the apples have cooled before covering them with the pastry.