Boil the milk on high heat. Set aside to cool slightly (77°C/170°F).
Mix the vinegar in one and three-fourth cups of water and add to the hot milk. Stir lightly till the milk curdles. Add three to four cups of cold water and a few ice cubes and stir.
Strain the chhenna through a piece of muslin and squeeze to remove all the water. You should have 250 grams of chhenna.
Transfer the chhenna onto a worktop. Mix together half a teaspoon of refined flour and the cornflour and add to the chhenna. Knead with the heel of your hands to a smooth mixture.
Divide the mixture into twenty-five equal portions and roll into oblong smooth rolls, taking care that there are no cracks. Make a small dent on one side and set aside.
Mix the remaining flour with half a cup of water and set aside.
To make the syrup, cook the sugar with five cups of water, stirring continuously till the sugar dissolves. Add the milk and let the syrup come to a boil. Collect the scum which rises to the surface with a ladle and discard. Continue to cook the syrup for a few minutes longer. Strain the syrup into a bowl.
Pour one cup of the syrup into a deep, wide non-stick pan and add four to five cups of water. When the syrup comes to a boil, add the chhenna rolls and half the flour-water mixture. The syrup will start frothing. Let the rolls cook in the syrup. Do not stir, but gently agitate the syrup so that the balls do not stick to the bottom of the pan.
Slowly drizzle half a cup of water along the sides of the pan every five minutes to prevent the syrup from thickening and forming strings. Continue cooking for fifteen minutes, or till the rolls spring back to their original shape.
Drain the rolls and soak in the reserved syrup. Chill for at least two hours so that the syrup is absorbed by the chhenna rolls.
For the topping, cook the khoya with the rose water, saffron, sugar syrup and yellow colour till the mixture thickens to the consistency of jam.