Yield: 8 to 12 servings
8 cups fresh blackberries (approximately 2¼ pounds)
2 cups fresh blueberries
¾ cup sugar
½ cup all-purpose flour
1⁄8 teaspoon salt
2 tablespoons fresh lemon juice
¼ teaspoon ground cinnamon
¼ cup cold butter, cut into small pieces
Buttery Pastry Dough
1 large egg, lightly beaten
1 teaspoon water
1 tablespoon sugar
Garnish: 1 teaspoon sugar
Vanilla ice cream (optional)
1. Preheat oven to 375°. In a 13x9-inch baking pan, combine blackberries, blueberries, sugar, flour, salt, lemon juice, and cinnamon, tossing gently. Dot with butter.
2. On a floured surface, roll 1 portion of Buttery Pastry Dough into a 9x6-inch rectangle. Cut crosswise into 6 strips. Place strips crosswise over fruit mixture in pan, trimming edges if necessary. Roll remaining portion of dough into a 13x4-inch rectangle. Cut lengthwise into 4 strips. Place strips lengthwise in pan, trimming edges if necessary.
3. In a small bowl, whisk together egg and 1 teaspoon water; lightly brush over dough. Sprinkle with sugar.
4. Bake until crust is golden brown and filling is bubbly, approximately 45 minutes. Garnish with 1 teaspoon sugar, if desired. Let stand for 20 minutes before serving. Serve with vanilla ice cream, if desired.