Ginger Miso Udon Noodle Soup with Roasted Mushrooms

Name: Ginger Miso Udon Noodle Soup with Roasted Mushrooms
Ingredients: 1 2-inch piece kombu (dried kelp); 1 cup dried bonito flakes; 2 tablespoons white miso paste; 1 teaspoon finely grated fresh ginger; 8 ounces shiitake mushrooms; 1 tablespoon soy sauce; 1 teaspoon sesame oil; 4 servings frozen udon noodles (you can also use dried, but trust me that frozen are so much better!); 4 baby bok choy, halved and steamed; 4 servings firm tofu, cut into cubes; sesame seeds and thinly sliced green onion, for garnish.