Bring soup to a boil. In a large pot, add water, beef, garlic, and green onion, and bring to a boil. Skim the scum off the surface. Once it reaches a boil, reduce the heat to medium, cover, and continue to cook for 30 minutes.
Make egg garnish. While the broth is cooking, heat 1 teaspoon of oil in a small pan over medium heat. Pour in the whisked egg yolk, then lift and tilt the pan to spread it across to form a thin crepe. Cook on both sides and transfer to a cutting board. Roll the egg and thinly slice it.
Slice the beef. Remove the beef and let it rest for 10 minutes before shredding into bite-sized pieces.
Add seasoning and rice cakes. Then add soy sauce, black pepper, sesame oil, and rice cakes. Cook the rice cakes until softened, about 3-4 minutes.
Serve. Garnish with the egg strips, seaweed, and green onion, and enjoy.