Preparation time 50 minutes (plus refrigeration time). Cooking time 1 hour 5 minutes.
1. Peel and core apples, slice thinly. Place in large saucepan with caster sugar; cook covered over low heat, about 10 minutes or until apples are just tender. Strain over small saucepan; reserve cooking liquid. Blend cornflour with the water, stir into reserved cooking liquid over heat until mixture boils and thickens. Place apples in large bowl, gently stir in cornflour mixture.
2. Meanwhile make pastry.
3. Toss blackberries in extra cornflour; stir gently into apple mixture.
4. Spoon fruit mixture into pastry case; top with rolled pastry. Press edges together, trim with knife; decorate edge. Brush pastry with a little water; sprinkle with demerara sugar. Using knife, make three cuts in top of pastry to allow steam to escape. Place pie on oven tray; bake uncovered, in hot oven 20 minutes. Reduce oven temperature to moderately hot; bake uncovered about 30 minutes or until pastry is browned lightly. Stand 10 minutes before serving.
Pastry: Blend or process flour, icing sugar and butter until combined. Add egg yolks and enough of the water to make ingredients just come together. Knead dough on floured surface until smooth. Refrigerate 30 minutes. Roll two-thirds of the dough between sheets of baking paper until large enough to line greased 23cm pie dish. Ease dough into dish; trim edge. Cover; refrigerate 30 minutes. Preheat oven to hot, roll remaining pastry between sheets of baking paper until large enough to cover pie.
Tip: This recipe is best made on the day of serving. For a different flavor, replace blackberries with blueberries, raspberries or strawberries.