Prepare the Filling: Peel, core, and chop all apples into ¾-inch chunks. Mix the lemon juice with cornflour to make a paste and add it to the apples. Heat gently in a saucepan, then add caster sugar, cinnamon, and ginger. Cook for 10 minutes on low heat, stirring regularly to avoid sticking. Once softened, remove from heat and stir in the Carnation caramel. Let the filling cool.

Make the Pastry: In a food processor, pulse plain flour, cinnamon, ginger, icing sugar, and butter until it resembles fine breadcrumbs. Gradually add the beaten egg and mix until it forms a ball. Wrap the pastry in cling film and chill for at least 30 minutes.

Preheat the Oven: Preheat the oven to 350°F (180°C, fan 320°F, gas 4).

Blind Bake the Pastry: Roll out ¾ of the pastry on a floured surface to about ¼-inch thick. Line a 9-inch pie dish with the pastry, leaving an overhang. Line the pastry with scrunched-up baking paper, fill with baking beans, and blind-bake for 20 minutes. Remove the paper and beans and bake for another 10 minutes until golden brown.

Assemble the Pie: Add the cooled apple filling to the baked pastry base, spreading it evenly.

Create the Lattice Top: Roll out the remaining pastry to about ¼-inch thickness and slice into ½-inch strips. Create a lattice pattern over the pie by laying the strips across the filling. Stick the strips to the pastry with beaten egg, trim off excess pastry, and brush the top with more beaten egg. Sprinkle demerara sugar over the top for a crunchy finish.

Bake the Pie: Place the pie on a baking tray and bake for 35-40 minutes until golden brown and bubbling. Keep an eye on it to avoid over-browning.

Serve: Let the pie cool for 15-20 minutes before serving. For a delightful treat, enjoy it with a scoop of vanilla ice cream!