Heat the milk in a large pot, if you have a thermometer, you are looking for 88° C (190° F), if no thermometer, heat the milk until you see bubbles on the sides and remove from heat.
After removing from the heat, gently stir the milk and slowly add the vinegar, once the vinegar is added, stop stirring and allow the milk to cool, about 30 minutes.
When cooled, pour the mixture, which is now curds and whey into a fine mesh colander and drain off the whey into another pot, allow to drain for about an hour. You can also line the colander with a clean cloth, cheesecloth, or a paper towel. I used a metal strainer with tiny holes, not a mesh strainer, use a spoon and move around in the curd, along the bottom of the strainer and the whey will drain, let it sit in the strainer for an hour or so, use the spoon every 5-10 minutes.
Pour the curds, this is the cheese part into a bowl, add salt and mix or enjoy or use as is in a recipe that calls for Cottage Cheese or Ricotta Cheese or as a side dish. Can be stored in the fridge for 2-3 days. In this photo you can see the cheese has thickened up as the whey is draining, and you can see the holes in the strainer.
For the firmer 'Farmer's Cheese' used in recipes, once you have the cottage cheese strained, line a large bowl with 2 or 3 layers of cheese cloth and pour in the strained cottage cheese, gather up the corners and tie that into a bag shape. Place a cutting board in your sink, place the tied up bag of cottage cheese on the cutting board, place another cutting board or large place on top of the bag, place some heavy canned goods on the top cutting board or plate to force out the remaining whey. After a few hours, Farmer's Cheese.
If using this as an ingredient, say for lasagna or another dish, use as is. If using as a side dish, sprinkle with a pinch of salt and mix that in.