The filling: only apple; it's added uncooked; is sweetened with caster sugar and bound with eggwhite and flour, so that when the apples cook, a glossy thick caramel sauce forms.
The pastry: this is a short one (read: tender, melt in the mouth), thanks to butter and sour cream. The top gets a demerara sugar sprinkle for a crunchy sugar lid.
To lattice or not to lattice? If an open weave is your thang, this sturdy sweet shortcrust, spiced with cinnamon, cloves and nutmeg is what you want.
That's not a typo, you read right: custard apple AND apple filling. This is a two-textured pie with a buttery, crumbly topping that has caramel notes from brown sugar.
A throw-it-together pie for the low-commitment baker.