- In a food processor, combine the flour, sugar and salt. Add the butter and pulse for a few seconds at a time until it is the size of small peas. Add the milk and egg yolk. Pulse until the dough just begins to form into a ball. Remove the dough from the food processor and form into a disc with your hands.
- Line a 43 x 30 cm (17 x 12-inch) baking sheet with parchment paper. On a floured work surface, roll out the dough into a rectangle the size of the baking sheet. Place on the sheet. Refrigerate for 30 minutes or freeze for 15 minutes.
- With the rack in the lowest position, preheat the oven to 200 °C (400 °F).
- In a large bowl, combine the icing sugar and cornstarch. Add the fruit and stir until the sugar has dissolved with the fruit. Scatter on the prepared dough, up to 5 cm (2-inches) from the edges. Fold the dough toward the centre.
- Bake for 30 to 35 minutes or until the crust is golden brown and the juices are bubbling. Let cool completely.
Off-season, if you can’t find blackberries, choose blueberries or strawberries, or just add a little more plums.