- Preheat oven to 450 degrees. In a large pot, cook barley according to packaging instructions.
- Clean mushrooms and cut into quarters (stems still attached). Finely chop the garlic, setting half aside. Remove thyme from stems, setting half aside.
- In roasting pan, toss mushrooms with ½ cup of oil, half of thyme, and half of garlic. Salt liberally. Roast mushrooms for 10 minutes While mushrooms are roasting, cut carrots and celery into ¼-inch cubes to make a mirepoix. Place the mirepoix in separate roasting pan, and toss with the remaining oil, thyme, and garlic. Roast for 6 minutes.
- Combine the cooked barley, mushrooms, and mirepoix, and garnish with parsley.