Make chenna: Heat 2 litres full-fat milk in a heavy pan until it comes to a rolling boil. Reduce heat to low and add 3 tbsp lemon juice or vinegar, stirring gently. The milk will curdle immediately.
Drain chenna: Line a colander with a thin muslin cloth. Pour the curdled milk through it. Gather the cloth and rinse under cold water for 1 minute to remove the acidic taste.
Squeeze and rest: Squeeze the cloth gently to remove excess water. Hang the chenna for 30 minutes to drain naturally. Do not over-squeeze — it should be moist and soft, not dry.
Knead chenna: Transfer chenna to a plate. Knead firmly with the heel of your palm for 8-10 minutes until it becomes smooth, soft and slightly greasy. This is the most important step.
Make sugar syrup: In a wide, deep pan add 2 cups sugar and 4 cups water. Bring to a rolling boil, stirring until sugar dissolves. Add 4-5 green cardamom pods and a few drops of rose water.
Shape rasgullas: Divide the kneaded chenna into 15-18 equal portions. Roll each between your palms into perfectly smooth balls with no cracks.
Drop into boiling syrup: Ensure the syrup is at a full rolling boil. Gently drop the chenna balls in. Cover the pan immediately.
Cook on high heat: Cook on high heat for exactly 15 minutes. The balls will nearly double in size. Do not open the lid for the first 10 minutes.
Check doneness: Press a rasgulla gently with a spoon — it should spring back. If it does not spring back, cook for 3 more minutes.
Chill and serve: Remove from heat and let the rasgullas cool in the syrup to room temperature. Refrigerate for at least 1 hour. Serve chilled — the syrup should be slightly absorbed into each ball.