1Heat oven to 350°F. Spray 2-quart casserole with cooking spray; set aside.
2On large cookie sheet, place bread slices. Bake 15 to 20 minutes, turning each slice once, until firm and very light golden brown. Remove bread slices from cookie sheet; cut into 1/2-inch cubes.
3In 12-inch nonstick skillet, heat oil over medium-high heat. Add celery, onion and carrot; cook 6 to 8 minutes, stirring frequently, until tender. Stir in broth, sage, salt, thyme and pepper; heat to boiling. Remove from heat. Stir in bread cubes until well mixed. Spoon mixture into casserole.
4Cover; bake 30 minutes. Uncover; bake 15 to 20 minutes longer or until hot and top is light golden brown.