Method

• 1.
  To make the dough, combine the milk and lemon juice in a jug (it will curdle, but will come together when combined with other ingredients). Place the flour and cornflour in a food processor and whiz to combine. Add the butter and pulse until starting to combine. With the motor running, add milk mixture and pulse until dough just comes together, with chunks of butter still visible. Divide into two even discs, wrap in plastic wrap and refrigerate for at least 1 hour.
• 2.
  If using fresh blueberries, place them in a bowl with the sugar and arrowroot and mix to combine.
• 3.
  If using frozen blueberries, thaw them, then place them in a large saucepan over medium heat and cook for 3 minutes, until berries let out some juice. Add the sugar and arrowroot and cook over medium-high heat, stirring gently, for 4 minutes, until mixture starts to thicken and darken in colour. Set aside to cool.
• 4.
  Preheat oven to 220°C/200°C fan-forced. Grease a 24.5cm x 18cm (base measurement) pie dish.
• 5.
  Roll out one disc of dough on a lightly floured work surface to a 30cm round, then use it to line the pie dish. Trim the overhanging pastry to 1cm, then freeze pie shell until needed.
• 6.
  Roll out the remaining pastry until 3mm thick and cut into 8 x 3cm-wide strips. Place on a baking paper-lined baking tray and chill for 30 minutes.
• 7.
  Transfer blueberry filling to the pastry shell. Arrange the pastry strips in a lattice pattern over the filling, pressing pastry sides and strips together to seal. Cut away any excess pastry.
• 8.
  Brush pastry with beaten egg, then sprinkle demerara sugar over the top. Place pie on a baking tray (to catch any spills) and bake for 20 minutes. Reduce oven to 180°C/160°C fan-forced and bake for a further 30-40 minutes, until pastry is golden and cooked through.
• 9.
  Remove from oven and cool on a wire rack until room temperature (see recipe notes). Serve with vanilla ice cream.