Cornbread, Sausage, and Pecan Dressing

INGREDIENTS

• 1 1/2 cups 1/4" slices celery
• 1 tablespoon chopped fresh thyme
• 3 cups low-sodium chicken broth, divided
• 2 1/2 cups chopped yellow onions
• 1 1/4 cups chopped toasted pecans (optional)
• 1 pound breakfast sausage links, casings removed
• 2 tablespoons chopped fresh sage
• 1/2 cup chopped flat-leaf parsley
• 1 tablespoon chopped fresh rosemary
• 2 large eggs
• 1/4 cup apple cider vinegar
• 1 teaspoon freshly ground black pepper
• 2 teaspoons kosher salt
• 3/4 cup (1 1/2 sticks) unsalted butter plus more for baking dish
• 1 pound day-old cornbread, broken into 1 1/2"-2" pieces (9 cups)