6 tablespoons unsalted butter, plus more for greasing dish
Kosher salt
12 ounces extra-wide egg noodles
10 ounces white mushrooms, halved or quartered
Freshly ground pepper
1/3 cup all-purpose flour
1 1/2 cups frozen pearl onions, thawed
1 medium carrot, halved lengthwise and sliced thinly across
1 large stalk celery, sliced thinly
2 sprigs fresh thyme
1/2 cup dry white wine or vermouth
4 cups chicken broth
1 cup heavy cream
2 cups shredded rotisserie chicken, skin and bones discarded
2 tablespoons chopped parsley
1 cup shredded Gouda (about 4 ounces)