Napa Cabbage And Udon Miso Soup

Ingredients

• 1 cup sliced dried shiitake mushrooms (about 1/2 ounce)
• 2 cups boiling water
• kosher salt
• 1 tablespoon vegetable oil
• 1/2 medium yellow onion, thinly sliced
• 1 tablespoon peeled and finely chopped fresh ginger (from about a 2-inch piece)
• 2 medium garlic cloves, finely chopped
• 6 cups low-sodium vegetable or chicken broth or stock
• 2 tablespoons soy sauce
• 1 (12-ounce) package udon noodles
• 1/2 medium napa cabbage (about 12 ounces), cored, halved lengthwise, and cut crosswise into 1-inch pieces
• 1/2 cup white miso
• 4 large eggs (optional)
• togarashi, for serving (optional)