Place the milk in a large pot over medium-low heat.
Let the milk warm gradually to 194°F or 90°C, monitoring the temperature with an instant-read thermometer. The milk should get lightly foamy, if it starts to boil, remove it immediately from the heat.
Once the milk temperature reaches the 90°C, remove the pot from the heat and pour in the lemon juice and season with sea salt.
Place a lid over the pot, and allow the milk mixture to sit for 10 minutes undisturbed. After this time the milk should start separating in clumps.
Set a strainer over a bowl and line the strainer with a cheesecloth. Scoop in the big curds out of the pot with a slotted spoon and transfer them to the strainer, then pour in the remaining curds.
Let the ricotta sit for 15 minutes up to 1 hour, depending on how creamy you want it to be.
You can eat the ricotta straight away or store it in an airtight container in the fridge for up to 2 days.
Notes
You can store fresh ricotta cheese in an airtight container in the fridge for up to 2 days.