Heat milk in a medium-sized, non-reactive (stainless steel, glass, enamel) pot over medium heat. Stirring occasionally, bring to 175 degrees (small bubbles will form around the edges).
Take off heat, stir in buttermilk and lemon juice. If curds don't begin forming right away add another 1-2 tsp lemon juice or vinegar. Let sit 10 minutes undisturbed.
Once curds and whey separate, ladle curds into cloth-lined colander. Tie ends of cloth together and hang 30 minutes over pot or sink to drain whey. Letting the cheese drain longer will create firmer cheese. Add salt, stir to incorporate.
Add herbs or flavorings as desired. Letting the cheese sit overnight will develop the flavor. Store in a covered, non-reactive container for up to one week.