Gently warm through the sour milk in a pan over a low heat until you see it beginning to curdle. You should see whey forming - this is when the water separates from the curds.
Remove the pan from the heat and set aside for 5 minutes to cool.
Drain off as much of the water as you can. Lay the cheesecloth inside the strainer over a large bowl.
Pour in the curds and leave to sit for a few minutes to allow any excess moisture to drip off.
Transfer the curds to an airtight container and mix in the salt and cream. Stir thoroughly and then place in the refrigerator for a few hours.