1
Combine the milk and the starter. Pour the milk into a pan of about 2.5 litres and add the soured milk or kefir. Whisk it properly, so the starter is spread through all of it rather than sitting in streaks. Cover it.
2
Leave it for 48 hours. Leave the covered pan at room temperature for around 48 hours. It is ready when it has set to a soft, even wobble, like a loose yoghurt, and smells clean and sour rather than sharp. Treat the 48 hours as a limit rather than a target: if it has not set and soured by then, throw it away and start again somewhere warmer rather than giving it longer.
3
Warm it to 50 C. Put the pan on the lowest heat you have and bring it up very slowly, whisking the whole time so the heat spreads evenly and the bottom does not catch. Take it off at about 48 C: the hot pan carries it up to 50 on its own. It will not look very separated at this point and that is fine, so do not push the heat to make it break.
4
Let it cool. Leave the pan alone for a couple of hours to cool down. This is where it separates: most of the curd gathers at the top and the whey settles underneath. The curds firm up as they cool too, and draining them warm loses more of them through the cloth.
5
Drain off the whey. Set a colander over your second pan and line it with the cloth. Pour everything in and let the whey run through, stirring gently with a spoon to help it along. Keep the whey.
6
Hang it up to drain. Gather the four corners of the cloth and tie them into a bundle. Hang it where it can drip freely with a bowl underneath, off a cupboard handle or a wooden spoon laid across a tall pot. After 3 to 4 hours, once the drip has slowed, move the bundle into a colander set inside a pot and put it in the fridge overnight rather than leaving it hanging out. For a firmer cheese you can slice, sit the tied bundle in the colander with something heavy on top for about two hours instead.
7
Turn it out. Untie the cloth and tip the cheese out onto a plate. Hung, it comes out as a soft dome that holds its shape and breaks into crumbs rather than smearing. Pressed, it is firmer and flatter, with the weave of the cloth printed across the top. Keep it covered in the fridge and eat it within 3 days.