Step 1
To make the pastry, process the flour, custard powder, icing sugar and butter in a food processor until the mixture resembles fine breadcrumbs. Add egg yolk and 1 tablespoon chilled water and process until dough just comes together. Shape into a disc. Cover with plastic wrap and place in the fridge for 30 mins to rest.
Step 2
Preheat oven to 200C. Reserve one-third of the dough. Roll the remaining dough on a floured surface to a 5mm-thick disc. Line base and side of a 22cm-round fluted tart pan with removable base with pastry. Trim edge, reserving excess pastry. Place in fridge for 15 mins to rest.
Step 3
Meanwhile, to make the caramel sauce, place sugar in a saucepan over medium heat. Cook, stirring, for 5-7 mins or until sugar dissolves and caramelises. Remove from heat. Add cream, butter and salt. Return to a low heat. Cook, stirring, for 3-4 mins or until the caramel boils and thickens. Set aside to cool.
Step 4
Combine apple and lemon juice in a bowl. Add brown sugar, flour, cinnamon, allspice and nutmeg. Arrange one-third of the apple mixture over the pastry case. Drizzle with 1 1/2 tablespoons of the caramel sauce. Continue layering with half the remaining apple and drizzle with 1 1/2 tablespoons caramel sauce. Top with remaining apple.
Step 5
Roll reserved pastry on a floured surface to a 3mm-thick disc. Cut into 3cm x 22cm strips. Arrange strips, cutting to fit, in a lattice pattern over the apple mixture. Place in the fridge for 15 mins to chill.
Step 6
Place pie on a baking tray. Brush pastry with egg and sprinkle with raw sugar. Bake for 30 mins or until golden. Set aside to cool slightly. Serve with vanilla ice-cream and remaining caramel sauce.