In a medium heavy-bottomed pot, heat the milk on the stove over medium-low heat until it reaches 180 degrees.
Add the lemon juice and salt to the milk and stir briefly to combine. Heat over a medium flame for a few more minutes until it reaches 200 degrees.
Remove the pot from the stove and let it sit for 10 minutes. The cheese will form as the curds separate from the whey. If you don’t see thick cheese forming in the first minute or two, add a little more lemon juice.
After 10 minutes, transfer the mixture to a fine mesh strainer lined with cheesecloth. I use this Butter Muslin, which is woven more tightly than some cheese cloth and it’s washable and reusable. (I use this to strain yogurt and ghee as well.)
Let the whey drain in the refrigerator until the ricotta reaches your desired thickness. Transfer the cheese to an air-tight container and store for up to 5 days.
You can alternately use plain white vinegar in place of the lemon juice.