In a large bowl, combine berries, white sugar and cornstarch, tossing to combine; set mixture aside for 15 min. Adjust oven rack to lowest position; place a rimmed baking sheet on the rack and preheat oven to 425°. Line a 9" deep-dish pie pan with 1 crust; fill with fruit mixture and dot with butter. Top with the second crust, tucking top crust under the edge of the bottom crust; pinch crusts together to seal. Flute edge of crust with fingers. Cut 6-8 slits in top of crust; brush with egg white and sprinkle with turbinado sugar. Place pie on the preheated baking sheet; bake until crust is a dark golden-brown (40-45 min.), covering the edges of the crust with strips of foil to prevent overbrowning in the last 10-15 min. if needed. Transfer pie to a wire rack; cool for 2 hrs. before serving.
- You can substitute 4 ½ cups of any type or combination of berries, including blackberries, for the strawberries, raspberries and blueberries called for in this recipe.