Baked Herb Stuffing

Name: Baked Herb Stuffing
Ingredients: 1 cup (2 sticks) unsalted butter, plus more for greasing pan; 2 medium yellow onions, finely chopped (about 3 cups); 6 medium celery stalks, finely chopped (about 2½ cups); 2 large eggs, lightly beaten; 1 (12–14-oz.) package instant stuffing mix; ⅓ cup finely chopped fresh parsley leaves, plus more; 1 tsp. dried sage, crumbled; ¼ tsp. Diamond Crystal or ¼ tsp. Morton kosher salt; ¼ tsp. freshly ground black pepper; 2¼ cups Homemade Turkey Stock, canned turkey stock, or chicken stock, heated until warm