In a large heavy bottomed pot, heat the milk over medium heat.
Add the salt and stir occasionally with a Wooden spoon. Do not let the milk scorch.
Heat the milk to 185° F.
If you do not have a thermometer, watch the milk for tiny bubbles that form around the edge of the pot. The milk should be steaming and there should be a slight thin film. This can take up to 20 minutes to get to this stage.
Reduce the heat to low and add your acid (lemon juice or vinegar)
Slowly stir the mixture for a couple of minutes, you should see the curds forming (this is the ricotta). The curds will separate from the whey (yellowish liquid).
Remove the pot from the heat and cover. Let sit for 20 minutes
While it is sitting, prepare your colander and cheesecloth. Dampen the cheesecloth then fold the it so that it covers the inside of the colander and has about 3-4 layers. Place the colander over a bowl. Do not use any reactive materials. Wooden spoons and glass or plastic bowls are best.
After the ricotta has sat for 20 minutes begin ladelling it into the prepared cheesecloth lined colander.
The consistency (creaminess) of the ricotta is dependent on how long you let the ricotta drain. For a creamier ricotta let it sit for only 3 or 4 minutes; for a drier ricotta, up to 20 minutes is fine.
Use immediately or cover and refrigerate until needed no longer than 3 days.