In a double boiler, gently heat cream to 190°F. Use a thermometer to avoid overheating.
While cream is heating, dissolve tartaric acid in 2 tablespoons of water.
Once the cream has reached 190°F, remove from heat and add the tartaric acid solution. Whisk thoroughly into the cream for 30 seconds.
Allow the cream mixture to sit for 5 minutes, stirring occasionally. The cream will thicken to a consistency similar to farina and should coat the back of the spoon.
Place a colander in a bowl and line the colander with sterile butter muslin or a sterile tea towel. Pour the coagulated cream into the cloth and let the whey drain for 1 to 2 hours or until the desired consistency is achieved. Spoon the mascarpone into a storage container and place in the refrigerator to chill. As it chills it will continue to thicken a bit. While mascarpone should be consumed within a day or two for optimal flavor, it can be stored in the refrigerator for up to a week.