A bowl of soba is a beautiful, exotic and delicious centerpiece for a Japanese meal: the not-too-soft, nutty buckwheat noodles sitting in a mahogany broth — dashi — that’s as clear and glossy as beef consommé, not only salty and umami-complex but sweet as well. My favorite variety, tamago toji, is egg-topped. When it’s made right, the egg is almost foamy, soft-scrambled and tender, deliciously flavored by the dashi, a bit of which it absorbs.