Pour the milk into a large saucepan. Dissolve the citric acid in a couple of tablespoons of cooled boiled water, then stir into the milk and add a pinch of salt.
Place the saucepan over a low heat. Frequently stir gently to prevent the milk scorching on the base of the pan while heating it.
Continue to heat until the milk has reached 85℃. During this time the milk will separate to small curds (solids) and whey (a yellowish liquid). Remove the pan from the heat, cover and allow to rest for 20 minutes,
Line a colander with muslin and pour the the mixture into the colander. Gather up the muslin to form a bag and suspend over a deep bowl or pan. Allow to drain for about 20 minutes.
Use the ricotta as required or spoon into a container, seal and store in the refrigerator for up to a week.
For a creamier cheese, stir in a couple of tablespoons of double cream, before chilling.