Japanese Squash-and-Soba-Noodle Soup

Bring water and kombu to a boil in a large saucepan. Remove from heat, stir in bonito flakes, and let stand 5 minutes. Pour broth through a fine sieve into a bowl, discard solids, and return broth to pan.

Add soy sauce, squash, and mushrooms to broth. Bring to a boil over high heat, reduce heat, and simmer, stirring occasionally, until squash is tender, about 10 minutes. Season with more soy sauce if desired.

Bring a large pot of water to a boil. Add noodles, and cook, stirring occasionally, until noodles are al dente, 5 to 7 minutes. Drain, and rinse under cold water.

Divide noodles among 4 bowls. Ladle soup over noodles, dollop with tofu, and garnish with scallions.