Bring a large amount of salted water to a boil, add barley and cook for 45 minutes or per package directions. Drain thoroughly and reserve. This should yield about 2 to 2-1/4 cups of cooked barley.
Heat the oil in a large, heavy pot or Dutch oven over medium heat, and add the onion. Cook, stirring often, until just about tender, about five minutes.
Add the sliced mushrooms. Cook, stirring, until the mushrooms are beginning to soften, about three minutes.
Add the garlic, 1/2 teaspoon of salt, thyme, a pinch of nutmeg. Continue to cook for about five minutes, until the mixture is juicy and fragrant.
Add the broth or water + bouillon. Add bay leaf. Stir, cover and bring to a boil, then reduce to a simmer and cook for 20 minutes.
Add the kale and simmer another 5 minutes.
At this point, your soup is almost ready to eat. One serving of soup requires 1-1/2 cup of this preparation + 1/4 cup of cooked barley. Separate and reserve the portion of soup you will not be eating right away, let it cool and refrigerate it.
Measure the appropriate amount of barley in proportion to the number of servings you will be eating. As an example, for 2 servings of soup, use about 3 cups of preparation + 1/2 cup of barley. Add the measured barley to the soup and heat it through for a few minutes just before serving. Add fresh ground pepper to taste.
Keeping the barley separate from the soup prevents is from soaking up more liquid while sitting in the refrigerator. Otherwise the next day your soup will become a soggy mush...