I originally intended this soup to be a sort of appetizer, but it can easily work as a main course soup. In fact, on a cold day a big bowl of this soup is all I need. It has light flavors in it but is really filling thanks to the soba and tofu. There are some spicy elements in the soup base, but I recommend dashing some hot sauce into it as well before digging in.
While I wrote this recipe to use cooked tofu, you can just press and cube uncooked tofu and toss it in. It will absorb f