Make the crust: In a large bowl, mix together ¾c all-purpose flour, the whole wheat flour, and salt. Add the butter and, using a pastry cutter (or your hands) work it into the flour until only pea-sized pieces remain. continue working with your hands until the dough is shaggy.
Add the water, starting with 3 tbsp and mix until the dough is moist enough to hold together. Add more water as needed, 1 tbsp at a time. Form the dough into a disc and wrap with plastic wrap. Refrigerate for 30-60 minutes
Preheat the oven to 190°c. Line a baking sheet with baking paper.
While the dough is resting, make the filling: In a medium bowl, combine the fruit, sugar and remaining 2 tbsp of flour. Toss to coat the fruit.
Assemble the crostata: on a lightly floured surface, roll the dough out to a 30cm wide circle, about 3mm thick. Transfer the dough to the prepared baking sheet.
Spoon the fruit filling into the centre of the dough, leaving a 5cm border around the edges. Fold the edges of the crust up and over the filling to create a rustic look. Brush the crust with the beaten egg and sprinkle with sugar.
Bake for 45-50 mins until the crust is golden brown.
Let it cool for 10-15 mins before slicing and serving.