Sterilise a large piece of muslin, cheesecloth (or a lint-free glass cloth like I used) by putting it into a pan/heatproof bowl and covering it completely with boiling water from a kettle
Using tongs, remove the cloth from the water and spread it over a metal colander
If you plan on using the whey, put the colander into a large mixing bowl so that all the liquid can be collected
Put the milk into a heavy-bottomed pan and heat to boiling stirring regularly to prevent it burning
When it begins to bubble, add the yoghurt and vinegar turn off the heat and stir. The curds should separate from the whey
Set aside until cool enough to handle
Pour the contents of the saucepan into the cloth covered colander
Remove the colander from the mixing bowl, put the colander into the kitchen sink and carefully rinse the curds
Sprinkle evenly with salt
Take up the corners of the cloth into your hands and twist & squeeze as much of the liquid out as possible
Form the cloth into a block shape
(I put the cloth into a DIY 'mould', a plastic container that some mushrooms came in that I punched holes in the bottom of)
Weigh it down with something heavy (I put a jar of dried split peas into an identical mushroom container and popped that on top)
Put the paneer on to an under-plate and refrigerate with the weight still on top for about half an hour
The paneer is ready to cut into cubes to be used or can be removed from the cloth, covered in cling film/saran wrap and left in the fridge for up to 5 days