Soak saffron strands in warm milk. Set aside while preparing the barfi mixture.
Add milk powder and milk in a heavy bottom kadhai. Turn on the heat. Start mixing till milk powder is nicely dissolved in milk. There should not be any lumps. This is STAGE 1.
Maintain gas flame between low to medium. Keep stirring the milk mixture, after a few minutes it will start thickening. This is STAGE 2.
Add cardamom powder and soaked saffron milk. Stir to combine in the barfi mixture. Keep stirring the barfi mixture. After 5 minutes, it will come together like a soft, non-sticky dough. This is STAGE 3. Turn off the heat.
Transfer the barfi mixture to a wide mixing bowl. Allow to cool down completely.
Once it is cool, add powdered sugar and mix nicely to form a dough.
Line a square glass tray or baking sheet with parchment paper. Transfer the barfi mixture into the tray. Press using a spatula to make a square shape of half inch even thickness. Cover and keep the barfi in the refrigerator for 1 - 2 hours or overnight.
Once barfi is set, cut it into equal size squares.
Serve mawa barfi immediately or store it in the refrigerator.