Keep 4 teaspoons of milk aside and boil the remaining milk in a heavy bottomed pan, stirring throughout, until it reduces to half. Warm the saffron in a small vessel, add 4 teaspoons of milk and rub until the saffron dissolves. Add to the boiling milk. Mix the citric acid in 3 teaspoons of water. Add this mixture very gradually to the boiling milk until it curdles slightly. This may require anything from half to the entire quantity of the citric acid mixture. Mix the cornflour in the balance 4 teaspoons of milk and add to the boiling mixture. Continue stirring till the mixture becomes thick and resembles khoya. Add the cardamom powder and mix well. Allow to cool. Add the sugar substitute and mix well. Shape into 7 small balls and serve, garnished saffron or pistachio.