The recipe is easy. The hardest thing is finding a piece of cheese-cloth.
Put all the milk in a large pan and bring to the boil. WATCH IT CAREFULLY! As soon as it boils it will start to froth - be ready. If your cooking with gas just turn it off but if it's an electric ring you'll have to lift the pan off and be quick about it. If you suddenly realise you haven't got the oven gloves handy then you're in trouble. You've been warned.
When the milk has boiled and you've turned the gas off or lifted the pan off the ring, add the lemon juice and stir. Return to the heat and continue stirring. The milk should curdle - that means there will be lots of white solid bits in a clear yellowish liquid. It should be obvious that this has happened but it may be that the milk has gone lumpy or grainy but the liquid is still white. This means your lemon wasn't big enough or wasn't acidic enough so it wouldn't hurt to have a spare lemon lying around when you try this.
Simmer and stir the mixture for four or five minutes (the longer you do this, the harder the final cheese will be) then pour it through a large piece of cheese-cloth which you have placed in a colander or sieve. The cloth should be large enough to hang well over the edges. Leave the curds (that's what the solid bits are called - the other stuff is called whey, probably because you pour it a-whey down the sink) to cool enough so that you can gather up the ends of the cloth without burning your hands. Twist the ends together to pack the curds into a ball and either squeeze the remaining liquid out with your hands or tie a piece of string round the gathered cloth and hang it up to drain. When most of the water has drained out, lay the cheese on an upside-down plate. Put another plate or a flat board on top and place something heavy on it to squeeze the cheese further. It's a good idea to put everything in a tray to catch the water that drains off. Leave the cheese for an hour or so to cool then unwrap it.
The paneer will keep in a plastic bag in the fridge for a few days, maybe even a week, but it can go sour if left too long.