This filling soup is enjoyed as a midday snack by many Japanese. Made to serve two, rather than four, you may find it sufficient for lunch or a light supper.
Over high heat, bring a large pot of water to a rolling boil. Scatter the buckwheat noodles across the water, cover, and return to a boil as rapidly as possible. Add the cold water, cover, and return to a boil again. Cook the noodles for 5 minutes, then test a strand: Place it in cold water to cool, then bite it. The noodle should be cooked through but still firm. If nec