1-Preheat the oven to 375°F (190°C) and line a baking sheet with parchment paper for easy cleanup.

2-In a large bowl, combine the flour and cold butter until the mixture resembles coarse crumbs for a flaky base.

3-Add 2 tablespoons of cold water and mix until a dough forms, then shape it into a disc and refrigerate for at least 10 minutes to improve handling.

4-In another bowl, toss the strawberries, raspberries, and blueberries with cornstarch, sugar, and lemon juice to create a thick, flavorful filling.

5-On the parchment-lined baking sheet, roll the dough into a 12-inch circle to form the crostata base.

6-Place the berry mixture in the center, leaving a 2-inch border, then fold the dough edges over the fruit for a rustic look.

7-Whisk the remaining cold water with the egg and brush it over the dough edges, then sprinkle sugar on top for a golden finish.

8-Bake for 30-35 minutes until the crust turns golden and the filling bubbles, then let it cool for about 5 minutes before serving warm.