Heat oven to 450 degrees F. Spray 10 1/2-inch cast iron skillet with no-stick cooking spray. Place in oven to heat. Beat egg in large bowl. Add remaining cornbread ingredients; mix well. Pour into hot skillet. Bake 20 to 25 minutes. Cool cornbread; crumble to make 6 cups; set aside. Reduce heat to 425 degrees F.
Spray 13 x 9-inch baking dish or pan with no-stick cooking spray. Melt butter in large skillet over medium heat. Add onions and celery; cook and stir until vegetables are tender.
Combine vegetable mixture, crumbled cornbread and remaining ingredients in large bowl; toss gently to mix. Add enough broth to make mixture very moist. Spoon into prepared baking dish or form into 12 oval cakes or pones; place in prepared baking dish. Bake 30 to 35 minutes or until golden brown.