• ¾ cup (1½ sticks) unsalted butter, plus more for baking dish
• 1 lb. good-quality day-old white bread, torn into 1" pieces (about 10 cups)
• 2½ cups chopped yellow onions
• 1½ cups (¼" slices) celery
• ½ cup chopped flat-leaf parsley
• 2 Tbsp. chopped fresh sage
• 1 Tbsp. chopped fresh rosemary
• 1 Tbsp. chopped fresh thyme
• 2 tsp. Diamond Crystal or 1 tsp. Morton kosher salt
• 1 tsp. freshly ground black pepper
• 2½ cups low-sodium chicken broth or vegetable broth, divided