Make the pastry: In a large bowl, rub the cold butter cubes into the flour, sugar, and salt using your fingertips until the mixture resembles coarse breadcrumbs. You should still see small, distinct flecks of butter—this is what creates a flaky texture. Slowly drizzle in the ice-cold water, one tablespoon at a time, mixing with a fork until the dough just comes together. It should feel cool and slightly shaggy, not wet or sticky. Gather it into a disc, wrap in cling film, and chill for at least 30 minutes.

Prepare the filling: While the dough rests, place the halved strawberries in a large bowl. Sprinkle over the granulated sugar, cornflour, lemon juice, and vanilla extract. Toss everything gently with your hands until the berries are evenly coated. You'll notice a glossy sheen forming as the sugar begins to draw out the juices. Set the bowl aside for 15 minutes—the smell of fresh strawberries and lemon will start to fill your kitchen.

Roll out the pastry: On a lightly floured surface, roll the chilled dough out to a circle about 30cm in diameter, turning it frequently to prevent sticking. The pastry should feel smooth and cold to the touch. Carefully transfer it to a 23cm pie dish, pressing it gently into the base and up the sides. Leave a slight overhang of dough around the rim.

Fill the pie: Spoon the strawberry mixture into the pastry case, including all the glossy, ruby-coloured juices that have collected in the bowl. The berries should mound slightly in the centre—they will settle as they bake. Fold the overhanging pastry edges back over the filling, pleating it loosely as you go to create a rustic, free-form edge. It doesn't need to be perfect; that's part of its charm.

Brush and sprinkle: Brush the exposed pastry edges generously with the beaten egg wash, using a pastry brush to coat every nook and cranny. Sprinkle the demerara sugar over the top—the sugar will caramelise in the oven, creating a beautiful, crunchy crust that shatters when you cut into it.

Bake to golden perfection: Place the pie on a baking tray to catch any drips. Bake in a preheated oven at 190°C (170°C fan) for 45-50 minutes. About halfway through, the kitchen will smell intensely of baked strawberries and butter. The pie is ready when the pastry is deep golden brown and the filling is bubbling thickly through the gaps—you'll hear a soft, steady hiss as the hot juices release their steam.

Cool completely: This is the hardest part. Transfer the pie to a wire cooling rack and allow it to cool for at least 3 hours. The filling needs this time to set into a firm, sliceable texture. If you cut it too soon, it will run all over the plate. Patience here is rewarded with clean, beautiful slices.