Dissolve the citric acid in the water. Bring the milk to a boil in a pan, stirring constantly, then remove from the heat and let it cool for 5-7 minutes until slightly warm.
Stir in the citric acid solution; the milk will curdle and the whey will separate. Let it rest for a few minutes, then strain through a damp cloth.
Gently squeeze the curd (chenna) caught in the cloth a few times to drain most of the whey, then knead until smooth.
Divide the chenna into 16 equal parts, and shape smooth balls with no cracks.
Bring the sugar, milk, and water to a boil in a large pan until the sugar dissolves. Skim off the grey foam that forms on the surface while boiling.
Mix the flour with a little water and pour it into the boiling syrup; once it foams, add the chenna balls.
Boil over high heat for about 15 minutes, sprinkling in a little water from time to time, until the balls swell and become springy.
Transfer the finished balls to a bowl with some of the syrup, and chill in the fridge for at least 3-4 hours before serving.