Place potatoes and carrots in a large saucepan; cover with water. Bring to a boil. Reduce heat; cover and simmer for 8-10 minutes or until crisp-tender. Drain and set aside. In a large skillet, saute onion in butter until tender. Stir in the flour, salt, thyme and pepper until blended. Gradually stir in broth and milk. Bring to a boil; cook and stir for 2 minutes or until thickened. Add the chicken, peas, corn, potatoes and carrots; remove from the heat.
Line two 9-in. pie plates with bottom pastry; trim even with edge of plate. Fill pastry shells with chicken mixture. Roll out remaining pastry to fit top of pies. Cut slits or decorative cutouts in pastry. Place over filling; trim, seal and flute edges.
Bake one potpie at 425 degrees F for 35-40 minutes or until crust is lightly browned. Let stand for 15 minutes before cutting. Cover and freeze remaining potpie for up to 3 months.
