Packaged mixes and store-bought cornbread vary in sweetness and moisture, so for this savory dressing, make yours from scratch. This simple buttermilk skillet version will give your dressing the best texture and flavor.
Preheat oven to 400°. Coat bottom and sides of a 10-inch cast-iron skillet with 1 Tbsp. oil; heat in oven 10 minutes.
Meanwhile, stir together cornmeal mix, next 3 ingredients, and remaining 1 Tbsp. oil. Pour batter into hot skillet.
Bake at 400° for 30 minutes or until golden. Remove from oven to a wire rack; cool 15 minutes. Crumble cornbread into a large bowl. Stir 5 cups broth into crumbled cornbread until moistened, adding more broth, 1 Tbsp. at a time, if necessary. (Mixture should resemble wet sand.)
Melt 1/4 cup butter in a large skillet over medium-high heat; add onion and celery, and sauté 8 to 10 minutes or until tender. Add onion mixture to cornbread mixture.
Microwave remaining 1/2 cup butter in a small microwave-safe bowl at HIGH 1 minute or until melted. Stir melted butter, eggs, and remaining ingredients into cornbread mixture; spoon into a lightly greased 13- x 9-inch baking dish.
Bake at 400° for 50 minutes to 1 hour or until golden brown. Serve immediately.