In a large pot, add 10 cups of water and all the broth ingredients. Bring it to a boil over high heat. Reduce the heat to medium low and boil for 10 minutes.
To make the egg garnish (jidan),* separate the egg and gently whisk each part. Heat a lightly oiled small nonstick skillet over medium heat and pour each egg part into a thin layer, tilting the skillet (similar to making crepe). Cook each side until no visible egg liquid remains. (Do not brown the egg.) Slice into 1 1/2-inch long thin strips or 1-inch diamond shapes. Set aside.
Slice the scallion into thin strips.
Return the broth to a boil over medium high heat and stir in soy sauce, salt and pepper to taste. Add the mandu, stirring gently so they don’t stick to the bottom of the pot. Boil until all of them float, and reduce the heat to medium and simmer for additional 2 or 3 minutes.
Ladle the steaming soup into bowls and garnish with the sliced egg and scallion.
Kimchi mandu is a popular choice for this soup, but you can use any type of dumplings for this soup, including pre-made store-bought dumplings.