Soak perl sago for and hour then wash all the starches from it by rinsing in water. Now cook them without mashing them. Wash the cooked perl sago until they stick starch is gone and only the individual transparent perl's are left.
In an blender add mango pulp, coconut milk, sugar and make a puree.
In bowl add mango puree, perl sago, mango pieces and keep in the freezer (refrigerator) for an hour and serve.
Instead of coconut milk you can use milk.
Adjust the sugar based on the sourness of the mango.