1 quart heavy cream
1/2 teaspoon Manischewitz sour salt
Pour cream into a heavy Dutch oven and set over low heat. Slowly heat the cream to 180 degrees F to 190 degrees F. (At 175 degrees F, start to keep a close watch.) Stir the cream a little. When the cream is ready, remove from heat. Sprinkle in the citric acid (sour salt), stirring gently twice. Wait until liquid stops moving and stir gently a few more times. Cover pot and let curds form for 30 to 40 minutes. The curds will firm up, but may not be obviously separated from the whey.
Meanwhile, line a strainer with damp cheesecloth and rest the strainer over a large bowl. Pour the cream through the strainer. Drain until mascarpone is room temperature. Cover the strainer, bowl and all, with plastic wrap to prevent refrigerator odors from getting into the delicate cheese and chill for 24 hours, to finish firming the cheese.
The mascarpone left in the strainer will be thick and creamy and ready to use. Transfer to a bowl and peel of cheesecloth. Keep refrigerated. Use within a week.
Makes 7/8 pound.