This recipe is pretty much straight from the magazine - I didn't modify it much, other than substituting a chicken stock cube for vegetable stock and dried thyme for the thyme sprigs, because that's what I had in the house.
2 T. extra-virgin olive oil
1 large onion, thinly sliced
2 leeks, white and tender green parts only, thinly sliced*
2 garlic cloves, minced
1 cup pearled barley
8 cups low-sodium vegetable broth
4 cups water
10 thyme sprigs (or 2 T. dried thyme)
2 bay leaves
1 1/2 pounds celery root (celeriac), peeled and cut into 1/2-inch cubes
1 pound parsnips, peeled and cut into 1/2-inch pieces
Salt and freshly ground pepper
1 pound baby spinach
1 t. grated nutmeg
Heat oil in a large (LARGE) pot. Add onion, leeks and garlic and cook over moderate heat, stirring occasionally, until tender, about 5 minutes. Stir in the barley. Add the vegetable broth and water, thyme, and bay leaves and bring to a boil. Add the celery root and parsnips and season with salt and pepper. Simmer over moderately low heat until the barley and root vegetables are tender, about 40 minutes. Stir in the spinach and nutmeg and simmer another 5 minutes. Season with a little more salt and pepper, to taste, and serve.
*I suspect that the American concept of leeks is very different from the British version, which tends to be a couple of inches in diameter, with thick, tightly wound concentric leaves. If you have robust leeks, you may want to slice lengthwise down them and then slice thinly crosswise. Or do as thou wilt. You have been warned.