Paneer is such a versatile ingredient to have on hand. I usually rely on the store-bought kind, since an indian grocery store is like two minutes away from my apartment. However, I had a fast dying container of 1% milk and the wastage police were behind me already... This is really a method and no specific amounts can be given. All the recipes that call for specific amounts of the acidic component have failed me. So here you go with approximate quantities:
Heat 4 cups of milk almost to the boiling point. You should see small bubbles around the container. Now add the acidic component- start with 2 tablespoon of lemon juice or 1 Tablespoon of the common vinegar. Stir. If the curdling begins already, stop stirring and continue heating for a minute more (without stirring) until all the curds have separated from the whey. If you don't see any separation, add another tablespoon of the curdling agent and stir to mix.
Off the record, I usually need about 1/4 cup of lemon juice to curdle 4 cups of milk. Vinegar is more powerful and 2 tablespoons of it may suffice. But vinegar gives its odor to the paneer. So you will be better off with lemon juice.
Now that the curds have separated, switch off your stove and add 1/4 cup of cold tap water. This is supposed to strengthen the cheese (or so I heard. Very important if you want to use paneer in bengali sweet delicacies). Place a double layer cheese-cloth on a strainer and pour the entire shebang into it. I save the liquid for cooking rice or pasta or for making bread softer. It contains a lot of nutrients and protein. Although it has an aroma of the curdling agent, it seems to melt into cooked dishes.
Make a bundle out of the cheesecloth and tie it to a faucet or hang it somewhere for 20 minutes until most of the liquid drips off. Press now and then to accelerate the process. Now place the cheesecloth clad paneer in a plate covered with paper towels. Place a heavy baking sheet on top and place several heavy cans over the baking sheet to press the paneer into a square or almost. Let this sit for 1 hour and then undress the paneer gently. Place the naked paneer in an airtight container or ziploc and refrigerate.
Update: This yielded 1 cup worth of paneer. Not much, but I have kept this in the freezer in a freezer-safe ziploc. I am sort of becoming a freezer queen, I know...