Stir together first 7 ingredients in a large bowl, stirring just until combined. Spoon into a lightly greased 13- x 9-inch baking dish.
Roll 1 piecrust to fit baking dish; place on top of berry mixture. Cut remaining piecrust into 1/2-inch strips. Arrange strips in a lattice design over piecrust. Brush with egg, and lightly sprinkle with 1 tablespoon sugar.
Bake at 400° for 55 to 60 minutes or until golden and bubbly.