In a pan, roast the sooji and besan together over low flame, stirring continuously for 5-6 minutes.
Add the ghee and continue cooking on low flame, stirring constantly until the mixture changes to a light chocolate brown color and becomes fragrant.
Add the sugar and mix it in. Slowly pour in the water while stirring continuously. Increase the flame. Be cautious as the mixture may bubble and splutter.
Keep stirring until the halwa thickens, and you see ghee starting to ooze out from the sides.
Garnish with slivered pistachios or almonds.
Video
Notes
Don't skimp on the ghee. It's important to roast the sooji properly.
Bombay sooji works best here because the grains are neither too big nor too small. Bansi rawa will also work.
Be patient and pay attention. Don't walk away and be prepared to spend half an hour in the kitchen. Sooji can burn pretty quickly if not stirred often or you can have uneven browning. So keep stirring every minute or so to make sure it browns evenly.
Add the sugar before the water or the sugar will caramelize and harden when it hits the water.