Pearl barley and dried mushrooms add body and texture, and a splash of white wine gives just the right amount of acid. Balanced with a handful of your favorite fresh herbs and a healthy shower of Parmigiano Reggiano, it's a one-pot meal that I go back to again and again when I need something warming and satisfying.
Using a fine mesh strainer, rinse the barley under cold, running water. Set aside.Remove and discard the stems of the mushrooms. Slice the caps, set aside.Remove the leafy parts of the kale leaves from the tougher stems. Tear or cut into bite-sized pieces, and set aside.
Using a sharp vegetable peeler, peel the butternut squash. Cut into 1/2-inch chunks, set aside.Peel and cube the carrot. Set aside.Peel, trim, and slice the garlic cloves. Set aside.
Set a large Dutch oven or heavy-bottomed pot over medium-high heat, and drizzle in half of the olive oil.Once the pot is hot, add the mushrooms. Saute for a few minutes until slightly softened and light brown in color. Add the kale, followed by the garlic. Stir until slightly wilted. Season with salt and pepper, to taste. Deglaze the pan with the cider vinegar, scraping up any browned bits off the bottom.
Pour the kale/mushroom mixture onto a plate, set aside.Place the pot back on the heat, drizzle in more of the olive oil, and add the carrots, squash, and pearl onions to the pot. Cook for a few minutes, to add a little color to the vegetables. Add the barley to the pot and stir and toast for a few seconds. Add the white wine to the pot and stir to scrape up any browned bits from the bottom of the pot. Cook until the alcohol has evaporated, about a minute.Add the dried mushrooms to the pot. Cover everything with the mushroom or vegetable stock. Season with salt and pepper, cover, and bring to a simmer. Continue to cook the soup until the vegetables have softened and the barley is cooked, about 25 to 30 minutes.
Add the kale/mushroom mixture back to the pot, and stir to combine. Taste the soup, and adjust the salt, pepper, and apple cider vinegar, if needed.Ladle the soup into a wide, shallow bowl. Garnish with freshly grated lemon zest, Parmesan cheese, and fresh horseradish. Finish with a few torn leaves of fresh herbs, and serve immediately.