Step 1Heat the milk and buttermilk in a heavy-bottomed pot over medium heat to a temperature of about 185 degrees. Stir in the salt and vinegar and remove from the heat. Let stand until curds have formed, 5 to 10 minutes. Pull the curds gently to the side
Step 2Line a strainer with cheesecloth and set it over a bowl. Using a perforated skimmer, gently lift the mass of curds out of the pot and into the cheesecloth-lined strainer. Repeat until no more curds remain. Discard the remaining whey.
Step 3Drain the curds for 5 minutes, then transfer to a covered container to store in the refrigerator until ready to use. The ricotta is best used the same day, but will still be good for 2 to 3 days.