Freshly ground black pepper
Kosher salt
1/2 cup Unbleached all-purpose flour
4 cups Finely chopped trimmed maitake or oyster mushrooms
2 cups Dry white wine
3 cups Lower-salt chicken broth
2 tablespoons Olive oil
2 Medium stalks celery, halved crosswise
1 Small yellow onion, quartered
1 tablespoon Crushed juniper berries
1/4 cup Finely chopped fresh flat-leaf parsley
Freshly ground black pepper
Kosher salt
10 tablespoons Unsalted butter, softened
16 pounds Fresh turkey, neck, tail, and giblets reserved for the gravy