Heat the oven to 375F.
Heat a large, ovenproof skillet over medium heat. Add ¼ cup olive oil, onion, celery, apples, garlic and sage. Sprinkle with ¼ teaspoon salt, stirring to combine. Cook, stirring occasionally, until the vegetables are softened, about 8-10 minutes.
Add the chopped cornbread, sprinkle with ¼ teaspoon salt, and stir to combine. Add the stock, stirring to allow the cornbread to absorb the liquid. Start with 8 oz of stock, then add more until the cornbread has absorbed the liquid and there's a little extra left in the pan.
Place the pan in the oven and cook, uncovered, until the liquid is absorbed and the stuffing is slightly browned, about 15-20 minutes.