In a heavy-bottomed pan, heat 1 liter of milk and bring it to a boil. Once it starts boiling, lower the heat and add 2 tablespoons of lemon juice or vinegar. Stir gently until the milk curdles completely.
Place a muslin cloth over a strainer and pour the curdled milk into it. Rinse the separated paneer (cottage cheese) with cold water to remove the sour taste of lemon juice or vinegar.
Squeeze the muslin cloth to remove excess water from the paneer and hang it for 30 minutes to drain any remaining whey.
Knead the paneer gently for 5-7 minutes until it becomes smooth and soft. Divide the paneer into small equal-sized balls.
In a separate pan, add 1.5 cups of sugar and 4 cups of water to make the sugar syrup. Bring it to a boil and let the sugar dissolve completely.
Gently drop the paneer balls into the boiling sugar syrup. Cover the pan and cook the rasgullas on medium heat for 10-12 minutes.
After 10-12 minutes, the rasgullas will expand in size. Turn off the heat and let them cool down in the sugar syrup.