Take sago in a bowl, soak it in water for 15 mins. Now drain it and add it in a pressure cooker, cover with water and pressure cook for 1 whistle. turn off the heat and let the steam go all by itself. Open the cooker, drain it and rinse it in lots of cold water, set aside.
Now take sugar and milk in a sauce pan and bring it to a boil. Once it boil, simmer and cook till it reduces a little.
Now add in the drained sago and cook for few more mins.
Take it off the heat and add in cardamom powder and saffron. Mix well.
Pour this in a bowl and chill till it is cold. It will thicken a lot.
Now take mango in a blender,puree smooth. Add this into the cold kheer, add chopped mangoes as well. mix well.