In a medium bowl, whisk together the flour, white sugar and salt. Add the butter and gently toss, evenly coating the cubes with the flour mixture. Place in the freezer for 10 minutes.

Transfer the flour-butter mixture to a food processor. Pulse until the butter chunks are about the size of peas, 10 to 12 pulses. Add the water and process until the mixture clumps together, but does not form a cohesive ball, 15 to 20 seconds.

Turn the dough onto the counter and press into a disk about 5 inches wide and 1 inch thick. Wrap tightly in plastic wrap, smoothing any crumbly or ragged edges. Refrigerate for at least 1 hour or up to 2 days.

About 1 hour before baking, heat the oven to 450°F with a baking steel or stone on the lower-middle rack. Line a rimmed baking sheet with kitchen parchment. Lightly flour the counter, unwrap the dough and set it on top. (If the dough is very firm, let it soften for 10 minutes.) Dust the top with flour and roll into a 12-inch round about ¼ inch thick, rotating frequently to prevent sticking and dusting with flour as needed. Drape the dough over the rolling pin and transfer to the prepared baking sheet.

Mound the berries in the center of the dough, leaving a 2-inch border. Sprinkle with 2 tablespoons of turbinado sugar.

Working with a 3-inch section at a time, fold the border of the dough onto the berries, leaving about ¼ inch of space between the berries and the inside of the fold. Pleat the dough as you go, then gently press the pleats to seal.

Lightly brush the dough with egg white, smoothing over any cracks, and sprinkle with the remaining 1 tablespoon turbinado sugar. Sprinkle the flaky salt over the crostata, then refrigerate uncovered for 10 minutes.

Bake until the crust is deep golden brown and the berries are bubbling, 25 to 30 minutes. Let cool on the baking sheet on a wire rack for 15 minutes. Carefully slide a metal spatula under the crostata to loosen it from the parchment. Serve warm or at room temperature.