How to Make It
Line a colander with cheesecloth and set it over a large bowl. In a large saucepan, combine the milk with the buttermilk. Cook over moderate heat, stirring occasionally, until the milk starts to separate and reaches 185° on a candy thermometer, about 5 minutes. Cook for 3 more minutes. Remove the saucepan from the heat and let stand for 10 minutes. Using a ladle, gently spoon the mixture into the prepared colander and let drain until the ricotta is thick, about 30 minutes. Transfer the ricotta to a medium bowl and season with salt; reserve the whey for another use.