Best Vegan Mushroom Barley Soup

Ingredients

• 1 ounce dried porcini or other dried mushrooms
• 2 cups hot tap water
• 1 1/2 pounds fresh mushrooms (button, shiitake, large or baby portobello, or a mix)
• 3 tablespoons olive oil
• 1 clove garlic, minced
• 1 large onion, diced
• 2 ribs celery, diced
• 2 carrots, diced
• 1 teaspoon salt
• 1/2 teaspoon black pepper
• 3/4 cup pearl barley
• 1 medium Yukon Gold potato, cut into 1/2-inch chunks
• 8 cups water, plus more if needed
• 2 tablespoons soy sauce, plus more to taste
• 2 tablespoons balsamic vinegar, plus more to taste
• 1 bay leaf
• 1/4 cup chopped fresh parsley
• 1/4 cup chopped fresh dill
• 3 ounces baby spinach (2 cups packed), tough stems removed