Method

Pastry

Put the flour, castor sugar, baking powder and butter in a food processor and pulse to combine. While the motor is running, add the ice water and the vanilla and process until it forms a smooth dough. Divide the dough into two equal parts, shape them into disks, wrap in plastic and refrigerate for 30 minutes. This pastry can also be made the day before.

Remove one disk of pastry from the fridge and place it on a lightly floured sheet of baking paper. Roll it out to about 3 mm thick and then flip it over into a 20 x 20 cm loose-bottomed tart tin. Carefully peel off the baking paper. Gently press the pastry into the tart tin and trim the edges, leaving a 5 mm overlap to allow for shrinkage. Place it in the fridge for 30 minutes to rest.

Preheat the oven to 180 °C. Line the prepared tart tin with baking paper and fill with baking beans. Bake blind for 15 minutes, remove the baking paper and beans and bake for another 5 minutes.

For the lattice top, remove the other disc of pastry from the fridge and place it on a lightly floured sheet of baking paper. Roll it out to about to about 2 mm thick and, using a pastry cutter, cut 10 strips measuring 30 cm x 2 cm.

Work as quickly as possible. Lay 5 strips of pastry horizontally on a clean sheet of baking paper, about 2 cm apart – these will be the bottom strips. Fold back every second strip to the left, lay the first top strip vertically about 2 cm in from the left and fold back the bottom strips. Fold back the other two bottom strips and lay down the next vertical strip. Fold back the bottom strips. Repeat the process until all the strips are placed. Slide the sheet of baking paper with the lattice topping on it onto a baking sheet. Place the lattice top in the fridge.

Filling

Combine the castor sugar, flour, lemon zest and juice, and the salt in a bowl. Add 150 g blueberries and crush them into the mixture with a potato masher to make a paste. Add the rest of the blueberries and toss them in the paste to coat them. Pour the filling into the cooked tart base.

To assemble

Remove the lattice top from the fridge, peel off the baking paper and carefully place it over the filling. Beat the egg, add the water, and mix well. Brush the top of the lattice with the egg wash. Sprinkle the castor sugar over the top of the lattice. Bake the tart for 35–40 minutes until the top is golden brown and the filling is bubbling.

Serve warm with clotted cream or vanilla ice cream.