Line a 9 inch pie plate with pastry as directed for double crust pie. Preheat oven to 400 degrees.
In large bowl combine blackberries and lemon juice; toss. In small bowl combine sugar and flour; sprinkle over blackberries and toss until well coated. Spoon into pastry-lined pie plate. Dot with butter. Top with remaining pastry.
In small bowl combine egg yolk and water. Brush evenly over top of pie. Bake about 1 hour or until juice bubbles through slits nearest the center. If edge gets too brown, cover with foil. Cool on wire rack. Makes 8 servings, about 500 calories each.
