Rinse the dried red beans thoroughly under running water until the water runs clear and no traces of dirt remain in the bowl. Add your dried red beans to a pot and cover them with cold water. Let them soak in cold water overnight or for at least 8 hours. Soak the rice cake for about an hour if you are using the frozen rice cake.
Add enough cold water to cover your soaked red bean. Once boiled, turn it to medium-low heat. Stir occasionally and boil until tender but not mushy, about 1 hour. The beans should be soft enough to mash easily with a spoon.
Add black rice, sweet potato, red dates, dried tangerine peels, and the soaked rice cake, along with rock sugar. Let the mixture continue to simmer for another 15 minutes or until it reaches your desired texture. Remove from the heat.
Add coconut milk or condensed milk over the red bean soup if you want more depth of flavor.
Serve warm and enjoy!