With Mango. The pairing of sago and mango is a very popular dessert combination. This pairing is not only rich and colorful, it is served in summer. To sago cooked. When cooking sago, you want the water to boil, sago into it, and cook it over medium-low heat for 10 minutes until it becomes transparent. Cooked sago should be rinsed with cold water to prevent sticking together and mango cut into small pieces. It has a sweeter flavor and softer texture. Put the mango flesh in a blender and puree.