Method

• 1.
  Preheat oven to 180°C. Line a 20cm pie dish with one of the pastry sheets, leaving a 1cm overhang. Line the pastry case with baking paper, fill with baking beads (or uncooked rice or dried beans) and bake for 15 minutes or until pastry is just dry and light golden. Remove paper and baking beads and leave to cool. Cut the remaining pastry sheet into eight 4cm strips. Chill strips while you make the filling.
• 2.
  Cook the rhubarb, vanilla, caster sugar and thyme sprigs with 1/4 cup (60ml) water in a large deep frypan over medium heat.
• 3.
  Carefully stir until sugar starts to dissolve, then reduce the heat to medium-low, cover and simmer for 8 minutes or until the rhubarb is almost tender. Using a slotted spoon, transfer the rhubarb to a colander set over a bowl and discard the thyme sprigs. Leave to drain very well.
• 4.
  Combine rhubarb syrup with cornflour and return to the pan set over medium heat. Boil for 10 minutes or until thick and syrupy. Set aside to cool completely.
• 5.
  Carefully fold rhubarb through syrup followed by the strawberries and balsamic vinegar. Spread cooled filling into pastry.
• 6.
  Make a tight lattice top with the chilled strips and place it over the filling. Trim any excess, pinching the edges to seal. Brush with the beaten egg and sprinkle with the demerara sugar. Place on a baking tray and bake for 55 minutes or until golden.
• 7.
  Rest for 30 minutes before serving.