PREPARE cornbread according to package directions for a double recipe, using broth in place of the liquid. Let cool 30 minutes before coarsely crumbling in a large mixing bowl; set aside.
PREHEAT oven to 400°F.
HEAT oil in a large nonstick skillet over medium-high heat. Cook sausage until browned, stirring frequently; remove and set aside.
ADD 1/2 cup of broth, celery, onion and sage to sausage drippings in skillet. Bring to a boil over medium-high heat; reduce heat to medium-low. Cover and cook 10 to 12 minutes or until celery is tender. Remove skillet from heat.
STIR sausage, celery mixture and black pepper into cornbread. Add remaining broth and egg; gently stir until just moistened. (For moister stuffing, add 1 cup additional broth.) Spoon into an 11x7-inch baking dish coated with non-stick cooking spray. Bake, uncovered, 25 minutes or until golden brown.