Remove piecrusts from freezer. Invert one crust onto waxed paper and let thaw until flattened. In medium saucepan, combine butter, flour, salt, thyme and pepper. Stir in broth and milk. Cook, stirring constantly, until mixture thickens and bubbles. Cook one minute longer. Then, stir in turkey, peas and carrots, celery and onion. Pour into the upright thawed piecrust. Moisten edge of crust with water. Preheat oven and cookie sheet to 425°F. Invert flattened crust on top of turkey pie. Trim edges and flute. Make slits in top for steam to escape. Bake 35 - 40 min. or until golden brown.