Dice the butter. Place the flour, caster sugar, butter, egg, baking powder and a pinch of salt into a food processor or mixer and blitz to a soft dough.
Transfer the dough to a floured surface and knead lightly into a ball. Cover with cling film and refrigerate for 1 hour.
Meanwhile, fill a bowl with water and squeeze the lemon into it. Peel the apples, cut into large chunks and put into the bowl of acidulated water to prevent them browning.
Put the sultanas into a small saucepan cover with the marsala and bring to the boil over a low heat for 5 minutes. Remove from the heat and set aside to cool.
PRE-HEAT OVEN TO 180˚C/160˚C FAN/GAS 4
Put the apples into a pan and sprinkle with the cinnamon and demerara sugar. Cover the pan with a lid and cook over a very low heat for 10 minutes, stirring frequently to prevent the apples sticking to the pan.
Transfer the cooked apple to a bowl, add the sultanas and set aside.
Grease a 20 x 20cm baking tray with a little butter.
Divide the pastry into two and roll out on a lightly floured surface. Lay one sheet in the prepared tray, spread the apple mixture over it and cover with the second sheet of pastry, making sure to seal the sides. Brush the top with a little milk.
Bake for 30 minutes. Switch off the oven and leave the crostata to rest for another 5 minutes.
Recipe Notes
This simple Italian pastry dish makes a fantastic dessert served with crème fraiche or our homemade custard. It is delicious served hot or cold.
You can substitute the apple filling with any other seasonal fruit you have at hand.