Combine flour, sugar, and salt in a mixing bowl. Add cold, cubed butter and cut in with a pastry cutter or fingers until the mixture resembles coarse crumbs. Gradually add ice water, one tablespoon at a time, mixing until dough begins to come together. Form into a disk, wrap in plastic, and refrigerate for at least 30 minutes.
1 1/4 cups all-purpose flour, 1/2 cup unsalted butter, 2 tablespoons granulated sugar, 1/4 teaspoon salt, 4-5 tablespoons ice water
Preheat the oven to 375°F (190°C). Roll out the chilled dough on a lightly floured surface into a circle about 12 inches in diameter. Fit the dough into a tart pan or baking dish, trimming excess edges. Prick the base with a fork to prevent bubbling.
Bake the crust blind by lining it with parchment paper and filling with pie weights or dried beans. Place in the oven and bake for 20 minutes until the edges are golden. Remove the weights and parchment, then bake for an additional 5 minutes to set the crust. Cool slightly.
Meanwhile, prepare the berry filling. In a bowl, combine berries, sugar, cornstarch, and lemon juice. Mix gently until berries are coated and the mixture starts to thicken slightly. Let sit for 10 minutes to allow flavors to meld.
2 cups mixed berries (strawberries, blueberries, raspberries), 1/4 cup granulated sugar, 2 tablespoons cornstarch, 1 teaspoon lemon juice
Pour the berry filling into the cooled tart crust, spreading evenly. Brush the edges of the crust with beaten egg wash containing water. Arrange some whole berries on top for visual appeal if desired. Bake the assembled tart for 20 minutes until filling is bubbly and the crust edges are golden brown.
1 egg egg wash, 1 tablespoon water
Remove the tart from the oven and let it cool to room temperature. Once cooled, arrange remaining fresh berries on top for garnish and a glossy finish. Serve slices with a dusting of powdered sugar or a dollop of whipped cream if desired.
