Bring a pot of water to a boil, add tapioca pearls (or sago). Cover and cook over a low heat for 15 minutes or so until the pearls are transparent but still have a white spot in the middle. Remove from the heat and set aside covered for a further 5-10 minutes until they are completely transparent (see note 1).
Meanwhile, prepare the fruit. Cut the flesh of mangoes into cubes. Set ¼ of them aside. Put the remainder of the cubes into a blender. Add coconut milk and cream (or milk). Blend to a very fine texture. Add some sugar if you prefer it a bit sweeter.
Peel grapefruit then gently separate the juice-packed sacs (see note 2).
When the tapioca pearls are ready to use, rinse them under cold water. Drain well, then place into serving bowls. Pour mango puree on top then garnish with the remaining mango cubes and grapefruit.
You may consume it immediately or chill in the fridge before serving.
Notes
1. Cooking time may vary depending on the size of the pearls. Please refer to the instructions on the package.2. Based on your own taste, you may adjust the amount of grapefruit required. Many places serve mango sago garnished with pomelo (a large citrus fruit which resembles grapefruit in flavour) instead. I prefer grapefruit for its more vibrant colour and its lightly acidic and bitter taste.