Preheat your oven to a cozy 350°F (175°C). Grab a large mixing bowl for your bread base.
Gently break your day-old buttermilk biscuits and cornbread into chunky pieces. Aim for about 8 cups of each. Place these crumbles into your large mixing bowl and set aside. Using day-old bread helps absorb flavors beautifully and prevents sogginess, making for a perfectly moist yet firm dressing.
In a large skillet (a cast iron one works great if you have it for easy serving!), melt about 2 tablespoons of butter over medium-low heat. Add your finely chopped celery and diced sweet onion. Sauté them until they become tender and translucent, about 5-7 minutes. Cooking gently helps release their natural sweetness.
Add the tender celery and onion mixture from the skillet to your bowl of crumbled breads. Mix everything well to distribute the veggies evenly.
In a separate saucepan, warm up the low-sodium chicken stock over medium heat. Stir in the poultry seasoning and dried parsley until well combined. Just before it boils, remove the saucepan from the heat.
Carefully stir the heavy cream into the warm chicken stock mixture. This creates a rich, flavorful liquid. For a slightly lighter option, you could use half-and-half here.
Slowly pour the hot liquid mixture over the bread and vegetable crumbles in your large bowl. Mix thoroughly but gently, ensuring all the bread pieces are well moistened. The mixture should be very moist but not watery. Taste and add salt and freshly ground black pepper as desired.
Transfer the dressing mixture into a 9x13 inch casserole dish or pat it down into your cast iron skillet. Dot the top with the remaining 2 tablespoons of butter.
Bake in your preheated oven for 40 minutes, or until the top is beautifully golden brown and delightfully crispy. Serve warm and enjoy your homemade holiday classic!