14-inch piece of kombu into 3 pieces. Using a damp cloth, wipe the
excess salt from both sides of the kombu sheet. Place the kombu and 5
cups water in a large covered pan and bring to a boil. Cover, leaving a
small opening, reduce the heat, and simmer over medium heat until the
liquid is reduced by one-quarter, or to 3.5 cups.
Add 1.5 cups
cold water, the carrots, onions, and celery to the kombu and broth.
Allow the water to return to a boil. Reduce the heat and simmer,
covered, over medium heat for at least 30 minutes. Strain and discard
the kombu and vegetables.