Preheat the oven to 400 F and spray a 9x9-inch baking dish with cooking spray.
In a medium mixing bowl, add the flour, cornmeal, sugar, salt, and baking powder. Whisk to combine well.
Make a well in the center of your dry ingredients and add ⅓ cup of melted butter, milk, and 1 egg. Mix until blended
Pour the batter into the baking dish and bake for 20 to 25 minutes, until the top is a deep golden brown and a toothpick inserted into the center comes out clean.
Let the cornbread cool for an hour then crumble it into a large Ziploc and leave unzipped on the counter for 24 hours.
When the cornbread has sat for a day, you can finish the recipe.
Preheat the oven to 400 F.
Melt the remaining butter in a frying pan and add the celery and shallots. Sauté for 5 minutes.
Put the crumbled cornbread into a large bowl and add the broth. Mix well. Add the poultry seasoning, sage, salt, and pepper.
Stir in the celery and shallots. Beat the remaining 2 eggs and add to the bowl.
Pour the dressing into a 9x13-inch baking dish and cover. Bake for 35 minutes. Remove cover the last 15 minutes so the top gets browned.