Sauté the Mushrooms: Warm 2 tablespoons of olive oil in a large, heavy-bottomed pot or Dutch oven over medium-high heat. Once the oil shimmers, add the sliced mushrooms. To achieve a deep brown color, arrange them in a single layer, working in two batches if necessary (adding a little more oil for the second batch if needed). Cook for 4-6 minutes on each side without stirring too frequently, until nicely browned and their moisture has released and evaporated. Transfer the cooked mushrooms to a separate plate and set aside.
Sweat the Aromatics: To the same pot, add the remaining tablespoon of olive oil (and the extra teaspoon if the pot seems too dry). Reduce heat to medium and add the diced onion, sliced carrot, and diced celery. Cook, stirring occasionally, for 5-7 minutes, or until the vegetables begin to soften and the onion is translucent.
Add Garlic and Deglaze: Stir in the minced garlic and cook for about 1 minute more, until fragrant, being careful not to burn it. Pour in the dry white wine, scraping up any browned bits from the bottom of the pot. Allow the wine to bubble and reduce by about half, which should take approximately 3-4 minutes.
Combine and Simmer: Return the sautéed mushrooms to the pot. Add the dried thyme, rubbed sage, and bay leaf. Pour in the vegetable broth and add the pearl barley. Increase the heat to high and bring the mixture to a rolling boil.
Cook the Barley: Once boiling, reduce the heat to low, cover the pot loosely (allowing some steam to escape), and let the soup simmer gently. Stir occasionally to prevent sticking. Cook for 40-45 minutes, or until the barley is tender yet slightly chewy. (See Note 1) If the soup becomes too thick during cooking, add a splash more hot water or broth to reach your desired consistency.
Season and Finish: Once the barley is cooked, remove the pot from the heat. Discard the bay leaf. Stir in the optional fresh lemon juice. Season generously with fine sea salt and freshly ground black pepper to your liking.
Serve: Ladle the Golden Harvest Mushroom Barley Soup into warm bowls. Serve immediately and enjoy this comforting dish.