Place a strainer or sieve over a medium bowl and line with 4 layers of cheesecloth. Set aside. Don’t have cheesecloth? Just use a sterile dish towel. You can sterilize a dish towel by placing the towel in a pot of water, bringing it to a boil and allowing the towel to dry. Squeeze your lemon to extract about 2 tablespoons of juice and set aside. Pour the 2 cups of heavy cream onto a heatproof bowl. In a small sauce pot add about an inch of water and over low heat bring it to a simmer. Place your heatproof bowl over the pot of simmering water. Insert your thermometer and heat the cream to about 180 - 185** degrees Fahrenheit, stirring often. Once you’ve brought your heavy cream to about 185 degrees, pour in the lemon juice and cook the cream until it thickens. The cream should coat the back of a spoon thickly. You will not see many whey streaks, and that’s OK. It supposed to look like a crème anglaise or ice-cream custard. Remove from heat and let it cool to room temperature. Once cool, pour the cream over the cheesecloth lined sieve and place in the fridge for 24 hours. Do not squeeze it. The whey will separate from the curd overnight and the mixture will thicken. Place in a container with a tightfitting lid and store in the fridge for up to a week. Makes about 14 ounces of mascarpone cheese. Notes: I wasn't able to bring heavy cream to 185 degrees no matter how long I stood over my stove. I got the cream to heat up to about 180 degrees, which still produced a smooth mascarpone.