Pour heavy cream into a saucepan over medium heat.

Use a spatula keep stirring it. To prevent the cream to stick at the bottom of saucepan.

Stir until it starts to boil.

Pour lemon juice into it until the cream become thick as it can coat the spatula.

Turn off the heat,transfer the saucepan to a bowl of cold water. Let it cool down about 20minutes.

Line a sieve with a piece of cheesecloth. A bowl is put under the sieve.

Pour the cream into the sieve then cover it.

Let it be in the refrigerator for about 8-12hours.

Then,your mascarpone cheese is ready! :D