Preheat your oven to 200°C (180°C fan) or 400°F. Line a large baking tray with baking paper. While the oven heats, prepare the filling. In a mixing bowl, combine the sliced strawberries, caster sugar, cornflour, lemon juice, vanilla extract, and a pinch of salt. Stir gently until the strawberries are evenly coated. You should see the sugar begin to draw out the juices, creating a slightly syrupy mixture that smells intensely sweet and fruity.

Prepare the pastry. On a lightly floured surface, unroll the sheet of puff pastry. Using a sharp knife, cut it into 8 equal rectangles. I like to trim the edges neatly for a cleaner look, but it’s not essential. The pastry should feel cold and firm to the touch.

Assemble the pastries. Spoon a generous tablespoon of the strawberry mixture onto the centre of each pastry rectangle, leaving a border of about 1.5cm around the edges. Be careful not to overfill, or the juices will leak out during baking. You want a mound of glistening berries in the middle.

Seal and glaze. Brush the exposed edges of the pastry with the beaten egg. Fold the pastry over to create a triangle or a rectangle, sealing the edges firmly with your fingers. Press the tines of a fork along the sealed edge to create a decorative pattern and ensure a tight seal. Brush the top of each pastry with more egg wash, then sprinkle with demerara sugar. The sugar will create a lovely crunchy, caramelised top.

Bake until golden. Place the pastries on the prepared baking tray, leaving a little space between them for air to circulate. Bake for 18–22 minutes, or until the pastry is puffed up and a deep, golden brown colour. The strawberry filling will be bubbling and fragrant. I always look for the edges to be a rich amber hue, and the kitchen will smell like a summer’s day.

Cool and serve. Remove the tray from the oven and let the pastries cool on the tray for 5 minutes. This allows the filling to set slightly and prevents burns. Transfer to a wire rack to cool completely, or serve warm. Dust with icing sugar just before serving for a beautiful, snowy finish.