If you are cooking with dry udon noodles, add them to salted boiling water and as soon as the water comes back to a boil, and 1 cup of cold water to the pot. Bring back to a boil again, add another cup of cold water. Continue doing this until the noodles are cooked. They should be tender with no hard core and have a slippery surface. Drain and immediately rinse the noodles in cold water to stop them from cooking more. Set aside and right before serving, rinse with boiling water. Place them in the serving bowls and then add the hot broth to them.