In a large pot, heat the sesame oil over medium heat.

Add the chopped onion and garlic, cooking until softened and fragrant, about 3-4 minutes.

Pour in the beef or vegetable broth and bring it to a simmer.

Add soy sauce, salt, and pepper to taste.

Carefully add the mandu to the simmering broth. Let them cook for about 5-7 minutes until they float to the top.

Stir in the chopped green onions and cook for an additional 2 minutes.

If using, beat the egg in a small bowl and slowly drizzle it into the soup, stirring gently.

Taste and adjust seasoning as necessary.

Serve the Mandu Guk hot in bowls, garnished with more green onions if desired.