Preheat your oven to 350 F. Generously butter a 9x13-inch baking dish, set aside.
Place a large sauté pan over medium-high heat. Heat the butter then add in the sausage. Cook the sausage in an even layer, stirring occasionally with a wooden spoon breaking it into bite-sized pieces until browned, about 10 minutes. Next, add the diced onion, celery and sage. Season generously with salt and pepper. Sauté for 5-7 minutes, stirring occasionally until the onion and celery are soft and translucent then turn off the heat and set aside.
While the sausage and onion mixture is cooking, use clean hands to crumble the cornbread into a large mixing bowl. The mixture should resemble coarse sand mixed with small and large bite-sized pieces. Next, add in the sausage, onion and celery mixture as well as the crumbled chestnuts.
In a separate bowl whisk together the stock, eggs and a few turns of freshly cracked black pepper. Pour over the cornbread mixture, toss to combine. Transfer the stuffing to the prepared baking dish, cover with foil. Bake, covered for 15 minutes then remove the foil and bake uncovered for 15-20 minutes or until the surface of the stuffing is lightly golden brown.