Mushroom and Wheat Berry Soup

Ingredients

• 1 cup wheat berries, rinsed
• 3 tablespoons cold-pressed extra-virgin olive oil
• 1½ pounds cremini mushrooms, trimmed and sliced thin
• Salt
• pepper
• 1 onion, chopped fine
• 6 garlic cloves, minced
• 2 teaspoons tomato paste
• 1 cup dry sherry
• 8 cups homemade or low-sodium chicken or vegetable broth
• 1 tablespoon low-sodium soy sauce
• 1 sprig fresh thyme
• 1 bay leaf
• ½ ounce dried shiitake mushrooms, finely ground using spice grinder
• 4 ounces mustard greens, stemmed and chopped
• ¼ teaspoon grated lemon zest