Heat milk slowly until just boiling, stirring frequently to prevent scalding. Add acid; stir gently and remove from heat. Let mixture sit for 10 minutes until curds settle below the liquid (whey).
Pour mixture into a cheesecloth-lined colander to separate curds from whey. Once it’s cool enough to handle, use the cloth to squeeze remaining moisture from solids. Discard liquid.
Unwrap cheese and place in a bowl. Stir in salt to taste. Knead by hand until smooth (not grainy); shape into a thick log. To store, cover in waxed paper and then plastic wrap; refrigerate.