Combine grapes, sugar, cornstarch, spices and salt; mix well. Place dough on baking sheet. Mound grape mixture in center of pastry, leaving a 3-inch border. Lift edges of dough up and over edge of grapes, leaving grapes showing in the center; fold edges of pastry to contain grapes. Combine walnuts, brown sugar and butter; mix well. Sprinkle over grapes. Brush pastry with milk. Bake at 375 F for 30 to 35 minutes or until pastry browns and the filling bubbles. Let stand 15 minutes before cutting.