Line a mesh strainer with cheesecloth and set over a deep bowl or pot.
Combine milk, cream, and salt in a heavy-bottomed saucepan and place over medium-high heat. Cook the mixture, stirring occasionally in a "figure eight" motion, until it reaches a temperature of 195 degrees F (90 degrees C). If you don't have a thermometer, this will be right before it starts to simmer. You'll see steam rising from the surface, and tiny bubbles forming around the edges of the pan.
Turn off the heat, pour in the vinegar, and stir slowly in a "figure eight" motion for 3 or 4 seconds.
Let the mixture sit, untouched, for 6 minutes.
Carefully ladle into the cheesecloth-lined mesh strainer so that the dripping whey drains into the pot or bowl. Let the ricotta drain into the pot for between 20 and 45 minutes, depending on how soft or firm you want your cheese. The longer it drains, the firmer the texture will be once chilled.
Grab the ends of the cheesecloth and lift the drained ricotta out of the strainer and place in a bowl. Let cool on the counter to room temperature, then wrap and chill thoroughly.
Remove cheesecloth and serve. Ricotta usually needs an additional pinch of salt when serving.