Prepare Vegetables: Slice the onion thinly. Peel and cut the sweet potato into small pieces. Soak the sweet potatoes in water for five minutes, then drain.
Sauté Onion: Heat the oil in a saucepan and sauté the sliced onion over low heat until tender.
Simmer: Add the sweet potato, water, and bouillon powder to the saucepan. Cover, bring to a boil, then simmer on low heat for 10 minutes or until tender.
Blend: Transfer the soup to a blender, add soy milk, and blend until smooth and creamy.
Finish: Return the soup to the saucepan and season with salt. Turn off the heat just before boiling. Serve in a soup bowl, and enjoy!
Notes
Storage: Transfer the soup to an airtight container and store it in the refrigerator. It can be stored for 3 to 4 days.
Japanese sweet potato skins are edible and packed with nutrients like other sweet potato varieties. While I usually cook them with the skins on, I peel them for this soup recipe to achieve a smooth, creamy white color.
Soaking sweet potatoes helps remove any bitterness and prevents them from changing or darkening in color.