4 cups mixed mushrooms (such as shiitake, maitake, oyster and beech), roughly torn
1 tablespoon thyme leaves
2 celery stalks, finely chopped
2 garlic cloves, minced
1 medium yellow onion, finely chopped
1 carrot, peeled and finely chopped
1 tablespoon flour
7 cups vegetable stock
1 cup pearl barley
2 tablespoons finely chopped parsley, plus more for garnish
1 tablespoon red wine vinegar
Kosher salt and freshly ground black pepper, to taste
Directions
In a small bowl, cover the dried porcini mushrooms with the boiling water and let soak until softened, 15 minutes. Drain, reserving the soaking liquid and roughly chopping the porcini.
In a large pot or Dutch oven, heat 3 tablespoons of the olive oil over medium-high heat. Add the mushrooms and thyme, and cook until golden brown, 6 to 8 minutes. Using a slotted spoon, transfer the mushrooms to a bowl.
Add the remaining tablespoon of olive oil to the pot. Add the celery, garlic, onion and carrot, and cook until softened and lightly caramelized, 5 minutes. Sprinkle in the flour and cook another 2 minutes. Slowly pour in the reserved soaking liquid and the stock, stirring constantly until incorporated. Add the soaked porcini, three-quarters of the reserved sautéed mushrooms and the barley, then bring to a boil. Reduce the heat to a simmer and cook until the barley is tender and the liquid is thickened, 35 to 40 minutes.
Stir in the parsley and vinegar, then season with salt and pepper. Divide between bowls and garnish with the remaining sautéed mushrooms and chopped parsley, then serve.