In a stainless steel, heavy-bottomed saucepan, bring the milk to a simmer over medium heat. Remove from heat and set aside until the milk is cooled. Whisk in the buttermilk.
Transfer the mixture to a glass, ceramic or plastic container, and set aside at room temperature until the mixture is thickened, with a consistency similar to yogurt or crème fraîche, about 1 day.
Transfer the mixture to a cheesecloth-lined strainer set over a bowl. Refrigerate overnight to drain the whey from the cheese; the whey should be clear, not cloudy, as it is drained.
Use as desired. To store, place the cheese in a glass, ceramic or plastic container. Cover and refrigerate up to four days.
Each of 20 tablespoons: 19 calories; 1 gram protein; 2 grams carbohydrates; 0 fiber; 1 gram fat; 1 gram saturated fat; 3 mg cholesterol; 2 grams sugar; 19 mg sodium.