– 1 1/4 cups all-purpose flour for the base of the flaky crust

– 1/2 cup unsalted butter (cubed and chilled) adds richness and helps form the dough

– 3 tablespoons cold water (divided) one part for mixing the dough and the rest for brushing

– 1 large egg acts as a binder and helps with browning the edges

– 1 1/2 cups sliced strawberries provides sweet and tangy flavor in the filling

– 1 1/2 cups raspberries adds a burst of tartness and color

– 1 cup blueberries contributes juiciness and antioxidants

– 2 tablespoons cornstarch thickens the filling to prevent it from becoming too runny

– 1/4 cup sugar sweetens the berries while helping with caramelization

– 1 tablespoon lemon juice enhances the tang and balances the sweetness