In a large bowl, whisk together cornmeal mix and salt. Add buttermilk and egg, stirring just until combined. Remove skillet from oven, and swirl to coat bottom and sides of pan with melted butter. Pour batter into hot pan. Bake for 20 to 25 minutes or until cornbread is golden brown and begins to pull away from sides of pan.
Pour the batter into the prepared baking dish. Bake until the top is golden brown and tester inserted into the middle of the corn bread comes out clean, about 20 to 25 minutes. Remove the cornbread from the oven and let it cool for 10 minutes before serving.
Instructions Preheat oven to 400°. Place butter in bottom of a 9-inch cast-iron skillet, and place skillet in oven to heat. In a large bowl, whisk together cornmeal mix and salt. Add buttermilk and egg, stirring just until combined. Bake for 20 to 25 minutes or until cornbread is golden brown and begins to pull away from sides of pan.