Combine first 4 ingredients; spoon into a 10- x 6- x 2-inch baking dish.
Combine flour, salt, and pepper in a heavy saucepan. Gradually stir in milk and broth. Cook over medium heat, stirring constantly, until thickened and bubbly. Pour sauce over chicken-vegetable mixture; top with Sweet Potato Crust. Turn pastry edges under; press firmly to rim of casserole to seal, and flute. (Make decorative design with excess pastry.) Cut slits in crust to allow steam to escape. Bake at 350° for 40 minutes or until crust is lightly browned.