Heat milk in a thick bottomed pan and bring it to boil. Keep stirring the milk so that the milk doesn't burn. Allow the milk to simmer for a minute before taking it off the heat.
Let the milk cool for 2-3 minutes before adding the lime juice, gradually add a teaspoon at a time. Once the milk is curdled, you will see the milk solids and the whey separate.
Line a colander with 2 layers of cheese cloth and set it down in the kitchen sink. Pour the curdled milk into the cheese cloth lined colander. Gather the edges of the cloth in your hands and squeeze out the whey.
Gently rinse the milk solids under running water so that the sour taste from the lemon juice is removed. Tie the ends of the cheese cloth to the kitchen faucet and allow the cheese to drain for about 30 mins to an hour.
Unwrap the drained chenna and transfer it to a clean plate/tray or a work surface. Knead the chenna with the heal of your palms for 10-12 mins or till its smooth. Add the sugar, saffron mixture and the cardamom powder and knead for 3-4 mins more.
Transfer the chenna mixture to a thick bottomed pan or wok and cook over low heat while mixing continuously.
Continue mixing till you see the chenna leaving the sides of the pan. This will take abut 10-12 mins. Ensure that the mixture is not completely dry. The mixture should be a little moist.
Take the chenna mixture off the heat and allow it to cool slightly. Divide the mixture into 15-20 portions. Grease your hands with a little ghee and shape each portion into a ball and flatten it slightly with your palms.
Garnish with sliced pistachios and serve immediately or store in an airtight container. Refrigerate and consume within 2 days of making it.