Prepare the Pastry: In a large mixing bowl, combine the plain flour, caster sugar, and a pinch of salt. Add the chilled, cubed unsalted butter. Using your fingertips or a pastry blender, quickly rub the butter into the flour until the mixture resembles coarse breadcrumbs with some pea-sized pieces of butter remaining. Gradually add the ice-cold water, a tablespoon at a time, mixing until the dough just comes together. Be careful not to overmix. The dough should feel cool and slightly firm. Divide the dough into two discs, wrap each tightly in cling film, and chill in the refrigerator for at least 30 minutes.

Make the Filling: While the pastry chills, prepare your filling. In a large bowl, combine the sliced peaches and diced mangoes. Sprinkle over the granulated sugar, cornflour, ground cinnamon, ground nutmeg, and lemon juice. Gently toss everything together until the fruit is evenly coated and the spices are fragrant, giving off a warm, sweet aroma. Set aside to allow the fruit to release some of its juices.

Roll Out the Pastry: Preheat your oven to 190°C (170°C fan/Gas Mark 5). On a lightly floured surface, roll out one disc of pastry into a roughly 30cm circle, about 3mm thick. Carefully transfer this pastry circle into a 23cm pie dish, gently pressing it into the base and up the sides. Trim any excess pastry, leaving a slight overhang. The pastry should look pale yellow and pliable.

Assemble the Pie: Pour the peach and mango filling into the pastry-lined pie dish, distributing the fruit evenly. Roll out the second disc of pastry to the same size. You can either place this as a solid top crust, or cut it into strips to create a lattice design. If making a lattice, weave the strips over and under each other for a classic look. The vibrant colours of the fruit will peek through beautifully.

Seal and Finish: Trim the edges of the top pastry, leaving about 1cm overhang. Fold the top and bottom pastry edges together and crimp them firmly to seal the pie. Brush the top crust with the beaten egg wash – this will give it a lovely golden sheen. Sprinkle generously with demerara sugar for a delightful crunch and sparkle. If you have a solid top crust, cut a few small slits in the centre to allow steam to escape.

Bake to Perfection: Place the pie on a baking tray (to catch any potential drips) and bake in the preheated oven for 20 minutes, or until the pastry starts to turn a light golden brown. Then, reduce the oven temperature to 170°C (150°C fan/Gas Mark 3) and continue to bake for another 25-30 minutes, or until the crust is a deep golden brown, and you can see the fruit juices bubbling thickly around the edges. A wonderful, sweet, fruity scent will fill your kitchen, signalling it's nearly ready. I've been making this for over 10 years, and this baking method never disappoints, ensuring a perfectly cooked filling and a crisp crust every time.

Cool and Serve: Once baked, carefully remove the pie from the oven and place it on a wire cooling rack. Let it cool for at least 30-45 minutes before slicing and serving. This resting time allows the filling to set properly, preventing it from being too runny. The crust will be firm to the touch, and the pie will be warm, not piping hot.