In a food processor, combine the flour, powdered sugar, and salt. Pulse a few times to mix. Add the chilled vegan butter cubes and pulse until the mixture resembles coarse crumbs.
Gradually add the ice water, one tablespoon at a time, and pulse until the dough just comes together when pinched. Be careful not to overmix. If the dough seems too dry, you can add more water, one tablespoon at a time.
Turn the dough out onto a floured surface and shape it into a disc. Wrap in plastic wrap and refrigerate for at least 30 minutes.
Preheat your oven to 375°F (190°C) and line a baking sheet with parchment paper
In a bowl, toss the mixed fruit with the granulated sugar, cornstarch, and vanilla extract until well combined.
On a floured surface, roll out the chilled dough into a circle about 12 inches in diameter and transfer it to the prepared baking sheet.
Spoon the fruit mixture onto the center of the dough, leaving about 1-2 inches of dough around the edges.
Fold the edges of the dough over the fruit, pleating as necessary to create a rustic, galette-like shape.
Optional: Brush the edges of the dough with a little plant-based milk or melted vegan butter for a golden finish.
Bake the fruit crostata in the preheated oven for 30-35 minutes, or until the crust is golden and the fruit is bubbly.
Remove from the oven and allow the crostata to cool on the baking sheet for a few minutes before transferring to a wire rack to cool completely.
Serve your vegan fruit crostata warm or at room temperature.