Soak the rice cakes in cold water in a bowl. (No need to soak if your rice cakes are freshly made)
Ina small sauce pan, heat the oil and brown the ground beef until no longer in pink over medium heat. Add the chopped onion and garlic and continue to cook until soft, about 3 minutes.
Add water, Korean soy sauce for soup, and anchovy sauce. Bring it to boil and simmer for 10 minutes over low heat covered but a slight opening to ventilate the steam. When done add freshly crack black pepper to the sauce. Set aside.
Mean while, bring a pot of water (8-10 cups) to boil. Drain the rice cakes from the soaking water and add to the boiling water. Cook the rice cakes over medium heat until tender and soft, about 3-5 minutes.
Ladle the rice cakes and some cooking water into a individual serving bowl. Place 2-3 tablespoonfuls of beef sauce and its juice on top. Top with green onion, sesame seeds, seaweed, and a drop of sesame oil. Serve hot with kimchi.