Prepare the oven: Preheat the oven to 350°F (175°C). Lightly grease a 7×11-inch baking dish or a similar-sized dish.
Add the cornbread: Place the crumbled cornbread in a large mixing bowl.
Cook the vegetables: Melt the butter in a skillet over medium heat. Add the diced onion and celery. Cook for 5–7 minutes, stirring occasionally, until the vegetables become tender and translucent.
Mix the dressing: Add the cooked vegetables to the crumbled cornbread. Pour in the chicken stock and beaten eggs. Sprinkle in the sage, then season with salt and black pepper. Stir until all the ingredients are evenly combined and the mixture is thoroughly moistened.
Bake: Transfer the mixture to the prepared baking dish and spread it evenly. Bake for approximately 30 minutes, or until warmed through and lightly golden around the edges.