Tip the flour and block margarine into a large bowl and rub together with fingertips until the mixture resembles breadcrumbs.
Stir through the icing sugar then vegan yoghurt and bring together into a soft dough. If the dough is a little dry or crumbly, add a little cold water at a time.
Chill the dough for 30 minutes whilst you make the filling.
For the filling:
Squeeze the juice of half a lemon into a large bowl. Peel and core the apples. Cut the eating apples into thick slices, and the cooking apples into smaller chunks. Put them into the bowl and toss through the lemon juice as you go, to stop them turning brown.
Stir through the light brown sugar, cinnamon, cornflour and sultanas.
To assemble the pie:
Preheat the oven to 180°C (fan) / 350°F / Gas Mark 4.
Tip the chilled pastry dough onto a floured surface and separate about a third of it to set aside for the lid. Roll the remaining two thirds with a rolling pin to roughly the thickness of a £1 coin.
Grease a loose-bottomed baking tin and line it with the pastry. Leave the edges overhanging for now.
Tip the apple filling into the pastry case.
Roll out the remaining pastry to make the lid. Wet the edges of the lid then place it on the top of the pie. Press the edges down firmly to create a seal, and cut a small hole in the top to allow steam to escape.
Use any leftover pastry to make decorations for the top of the pie - roll these as thinly as you can.
Brush the pie lid all over with dairy-free milk to glaze.
Sprinkle with a little caster sugar then bake for 35-45 minutes until golden. Serve warm with vegan ice cream or custard.