Our (my MIL taught me this) version-
Roast makhanas for a few minutes. The makhanas will become harder and make hollow sounds while roasting. This shows they are done. Let it cool.
Pulse them for a few mins in the food processor.
To make kheer-
Put milk for boiling. Separate one bowl while its lukewarm. Take the makhana powder and mix in the lukewarm milk. Add this to the boiled milk. Roughly, 1 cup powder for 1 litre milk. Let it simmer for a few minutes. It will be flowy but thickens when it cools down.
Add sugar (jaggery doesnt taste good with this) and broken cashews and raisins. Serve cold only!