For the cornbread:

1. Grease a 10″ cast iron skillet and place on center rack in the oven.
2. Preheat oven to 425°F.
3. In a large mixing bowl, stir together cornmeal, flour, sugar, baking powder, and salt. 
4. In a separate bowl, whisk the eggs, melted butter, and buttermilk.
5. Add the wet ingredients to the dry ingredients and stir.
6. Pour the batter into the preheated skillet and smooth. Bake until cornbread is golden yellow (about 16 to 19 minutes). Immediately remove the cornbread from the skillet and allow it to cool completely.
7. Crumble the cooled cornbread and set aside.

For the stuffing:

1. Preheat oven to 350°F.
2. Combine the cornbread with the stuffing mix in a large mixing bowl and toss to combine.
3. Melt 1 stick butter in a large skillet over medium heat. Add the onion and celery and sauté, stirring frequently, until soft and translucent (about 10 to12 minutes).
4. Add the onion and celery to the cornbread mixture.
5. In a large mixing bowl, combine melted butter, chicken stock, eggs, and sage, and whisk to combine. Add to the cornbread mixture and mix. Season generously with kosher salt and pepper.
6. Pour mixture into a greased 9 x 13-inch casserole dish.
7. Bak for 45 minutes to 50 minutes.