Boil 1/2 litre of milk. As it comes to a boil, switch off the flame. Add vinegar and keep stirring gently till the milk curdles.
Line a big bowl with muslin cloth or cheesecloth. Drain the chana and whey mixture through it. Strain the whey and wash the chana with cold water 2-3 times to remove the vinegary smell.
Tie the chana in the muslin cloth and hang till all the water has drained for 45 minutes.
Take out the chana in a bowl and crumble and lightly mash it using your fingers.
Boil the rest of the milk in a thick bottomed pan. Add the elaichi powder and let the milk simmer on low heat till reduced to almost one third.
Throw in the mashed chana and sugar, give it a hearty stir and let it simmer over low flame for another 15-20 minutes till it thickens a bit. If you like it sweeter, feel free to indulge - add some more sugar !!
Take off the heat. Add the rose water and allow to cool. The Chanar payesh is ready to serve.