Pour the milk into a large pan and heat to 85 degrees C. Add the salt, if using, and stir to dissolve. Add the vinegar a little at a time, stirring gently until the curds separate.
Dampen the cheesecloth and use it to line a colander. Using a slotted spoon, ladle in the curds. Fold the cheesecloth over the curds and cover with a weight, such as with a small plate with a container of water on top. Let the water drain out for 1-3 hours.