Take a pan and add milk in it. Give one boil to the milk then turn off the heat and wait for 2-3 minutes.plate and mash it well with hands.
Milk water and vinegar and add a little at a time while mixing it continuously till milk curdles up completely. Take a large bowl, put a sieve on it and then put a muslin/cotton cloth on it.
Strain the water and chhena through it, after that wash it well with room temperature water while mixing it.
Remove the cloth with chhena and dip a few times in water and squeeze the excess water out.
Once dry remove the chhena on a plate and mash it well with hands.
In a large pan add milk, stir and cook on low flame till it becomes thick or reduces to ¼.
After it reaches its desired thickness add sugar, little at a time while stirring it continuously.
Now increase the flame to full and add rest of the sugar while stirring it. Cook for 5-6 minutes while stirring continuously.
Once sugar dissolves completely, reduce the flame to medium and cook again for 4-5 minutes while stirring it.
After 5 minutes add cardamom powder and mashed chhena in it, mix well and keep cooking on medium flame.
If you want to serve like rabri then you can stop after cooking chhena with rabri for a few minutes and garnish with nuts and serve. If you want to serve like barfi then cook for afew extra minutes.
Once mixture looks thick enough turn off the flame and keep stirring for a few minutes.