01 -  In a large bowl, whisk together flour, sugar, and salt. Add the cold butter and blend using a pastry cutter or fingertips until the mixture forms coarse crumbs. Gradually add ice water, mixing until the dough just holds together. Shape into a disk, wrap in plastic, and refrigerate for at least 30 minutes. 
 02 -  Preheat oven to 200°C. Line a baking sheet with parchment paper. 
 03 -  In a medium bowl, gently toss blueberries with sugar, cornstarch, lemon zest, lemon juice, vanilla, and a pinch of salt. Set aside. 
 04 -  On a lightly floured surface, roll the chilled dough into a 30 cm circle. Transfer to the prepared baking sheet. 
 05 -  Mound the blueberry mixture in the center of the pastry, leaving a 5 cm border. Fold the pastry edges up over the filling, pleating as necessary. 
 06 -  Brush the pastry edges with beaten egg and, if desired, sprinkle with coarse sugar. 
 07 -  Bake for 35–40 minutes, or until the crust is golden brown and the filling is bubbling. 
 08 -  Allow to cool for at least 15 minutes before slicing. Serve warm or at room temperature.