Pour cream into a heavy bottom saucepan over medium heat.
Clip a candy thermometer to the pot, being sure that the probe touches the cream.
Cook, stirring frequently to prevent scorching, until the cream reaches 190°F.
Add the lemon juice to the pot and stir to combine.
Continue cooking, stirring constantly with a rubber spatula, for another 5 minutes, maintaining the temperature at 190°F. The mixture will thicken.
Take the pot of mascarpone off the heat and allow it to cool to room temperature.
Line a fine mesh sieve with multiple layers of cheesecloth and place it over a bowl.
Transfer the thickened cream into the lined sieve and refrigerate it, with the bowl underneath, for at least 8 hours.
Use a spatula to scrape the mascarpone from the cheesecloth into an airtight container.
Cover and store in the refrigerator for up to 1 week.
