If making cornbread from scratch, bake according to your recipe and allow it to cool completely. Alternatively, use pre-made 9-inch cornbread.

Crumble the cooled cornbread into a large mixing bowl, then add the cubed stale white bread and toss gently to combine.

Preheat the oven to 350°F (175°C) and spray a 9x13-inch baking dish with cooking spray.

In a large skillet over medium heat, melt 4 tablespoons of the butter. Add the chopped onion and celery and sauté until they are softened, about 6–8 minutes. Season with salt and pepper, then transfer the vegetables to the bowl with the bread mixture.

Melt the remaining 6 tablespoons of butter in a separate bowl or small saucepan. Whisk together the melted butter, broth, eggs, chopped sage, and a pinch of salt and pepper until evenly combined.

Pour the egg-broth mixture over the bread and vegetable mixture. Stir gently but thoroughly so the bread soaks up the liquid and ingredients are evenly distributed.

Transfer the combined mixture into the prepared baking dish, spreading it into an even layer. Bake in the preheated oven for about 45 minutes, or until the top is golden brown and the center is set.

Remove from the oven, sprinkle with chopped parsley, and garnish with sage leaves if using. Let rest briefly, then serve warm.