In a large mixing bowl, combine the flour and butter and mix together until coarse crumbs remain. Add two tablespoons of water and mix together until a thick dough remains.
Shape the dough into a disc and refrigerate for 10 minutes.
In a small bowl, add the berries, then toss through the cornstarch. Add the sugar and lemon juice and mix well.
Preheat the oven to 190C/375F and line a cookie or baking sheet with parchment paper.
Roll the crostata dough into a 12-inch circle onto the lined sheet. Place the berry mixture into the center, reserving two inches from the sides. Fold the dough over the fruit.
Whisk the egg with the remaining tablespoon of water and brush around the dough. Sprinkle with the sugar.
Bake the crostata for 30-35 minutes or until golden.
Let the crostata sit for 5 minutes before slicing.
Notes
TO STORE. Keep the leftover crostata at room temperature for a day. If you wish to store it for longer, store it covered in a refrigerator for 2-3 days.TO FREEZE. Crostata freezes well. Wrap it in a freezer-safe bag and store it in the freezer for three months. When you’re ready to eat, thaw it out inside the refrigerator.