- 1 medium onion, chopped
- 2 garlic cloves, chopped
- 1 tablespoon olive oil
- 1/2 pound fresh shiitake mushrooms
- 1 teaspoon chopped thyme
- 1 (14 1/2-ounce) can diced fire-roasted tomatoes
- 1 qt vegetable stock or broth
- 3/4 cup quick-cooking barley
- 5 ounces baby spinach (8 cups)
- 1 tablespoon distilled white vinegar (optional)
- 4 large eggs (optional)
- Garnish: grated Parmigiano-Reggiano
- Cook onion and garlic with 1/2 teaspoon salt in oil in a large heavy saucepan over medium heat, stirring occasionally, until pale golden, about 10 minutes.
- Meanwhile, discard stems from mushrooms. Halve caps, then thinly slice crosswise. Add mushrooms and thyme to onion and cook, stirring occasionally, until mushrooms are softened, about 5 minutes. Stir in tomatoes with their juice, stock, barley, and 1/2 teaspoon each of salt and pepper and simmer briskly, covered, stirring occasionally, until barley is tender, 10 to 15 minutes. Stir in spinach and cook 1 minute, then season with salt.
- Meanwhile (if using eggs), bring 2 quarts water to a simmer with vinegar and 1 tablespoon salt in a wide medium saucepan.
- Break 1 egg into a cup and slide into water. Repeat with remaining eggs, spacing evenly. Poach at a bare simmer until whites are firm and yolks are still runny, 2 to 3 minutes. Transfer to paper towels using a slotted spoon.
- Serve soup in bowls, topped with eggs.