Step 1

Fill a medium pot about two thirds of the way with water, and bring it to a rolling boil. Stir in the sago (don’t add it before the water is at a full boil!). Simmer for 20 minutes, or until the tapioca is completely translucent, which means it’s fully cooked. If after 20 minutes, the pearls still have a white center, turn off the heat, cover, and let the tapioca sit in the hot water for another 5-10 minutes, or until they’re fully translucent. Drain through a fine-mesh strainer, rinse in cold water to cool, then soak in a bowl of cold water and set aside.

Step 2

Take your taro and cut it in half or thirds crosswise. Place the taro pieces flat side down, and use your knife to carefully cut away the outer skin. Dice about 1 cup (5 ounces) of taro into ¼-inch cubes. Cut the remainder of the taro into larger 1-inch chunks.

Step 3

Add 7 cups of water to a large pot along with the bigger 1-inch taro chunks and the rock sugar. Bring to a boil, cover, and simmer over medium heat for 20 minutes, or until the taro is very tender.

Step 4

Use a potato masher to mash the taro until relatively smooth. The soup will appear somewhat thin at this point; it will thicken as it continues to cook.

Step 5

Stir in the sweet potato and taro cubes. Bring to a low simmer, cover, and cook for another 10-12 minutes, stirring occasionally to prevent sticking or burning, until the taro and sweet potato cubes are tender.

Step 6

Stir in the coconut milk, sweetened condensed milk, salt, and vanilla (if using). Cook for another 2 minutes.

Step 7

Drain the sago, and stir it into the soup. If the soup is too thick, add boiling water until you get the consistency to your liking. Serve!