Add mirin, soy sauce, sugar, salt and sesame oil (if using) and stir to combine.
Add udon noodles. If using shelf-stable noodles allow the blocks to sit in the stock for a minute before gently separating the noodles. Gently boil stock and noodles fr 3 minutes.
Divide soup into bowls and garnish with sliced scallions or other garnish.
Notes
See the "How To Make This" & "Tips For Success" sections above the recipe for more detailed information on the process.