Prepare the Dough: In a large bowl, combine the 400g of plain flour, 200g of caster sugar, 1 tsp of cinnamon, and a pinch of salt. Add the 250g of cold, cubed butter. Using your fingertips, rub the butter into the flour mixture until it resembles coarse breadcrumbs.

Form the Pastry: Add about two-thirds of the beaten egg to the flour mixture (reserve the rest for an egg wash). Gently bring the mixture together with your hands to form a soft dough. Don't overwork it. Take two-thirds of this dough, wrap it in cling film, and chill in the fridge for 30 minutes. The remaining one-third is your streusel base - just leave it in the bowl.

Prepare the Tin: Grease and flour a 23cm (9-inch) deep springform tin. Take the chilled dough from the fridge and press it evenly over the base and about two-thirds of the way up the sides of the tin. What works best for me is using the flat bottom of a glass to press the base down firmly and evenly. Prick the base with a fork and pop it back in the fridge while you make the filling.

Make the Apple Filling: Peel, core, and slice your apples into chunks about 1-2 cm thick. Place them in a large bowl and toss with the lemon juice immediately to prevent browning. Add the 75g of light brown sugar, 50g of raisins (if using), 1 tsp of cinnamon, the nutmeg, and the tbsp of cornflour. Toss everything together until the apples are evenly coated.

Assemble the Pie: Preheat your oven to 180°C (160°C fan/Gas Mark 4). Take the pastry-lined tin from the fridge and pile the apple filling inside. It will seem like a lot, but they will cook down. Gently press them down to pack them in.

Add the Streusel: Take the remaining third of the dough mixture you set aside. Simply use your fingers to crumble it evenly over the top of the apple filling, creating a rustic, bumpy streusel topping.

Bake to Perfection: Brush the exposed rim of the pastry with the leftover beaten egg. Place the springform tin on a baking tray to catch any drips. Bake for 60-70 minutes, or until the streusel is a deep golden brown and the apple filling is bubbling. If the top starts to brown too quickly, you can loosely cover it with foil for the last 15 minutes.

Rest the Pie: This is a crucial step! Once baked, remove the pie from the oven and let it cool completely in the tin on a wire rack. This will take at least 3-4 hours. This allows the filling to set properly, ensuring you can cut clean slices.