Place the milk and salt in a saucepan over medium-high heat until the mixture reaches a consistent simmer (but not boiling). Remove from the heat and stir through the lemon juice. Gently stir three or four times and then return to a low heat for another 1 minute before removing again. The mixture will immediately start to separate into curds (the ricotta) and whey, and will continue to do so over a period of about 15 minutes.
After 15 minutes, pour the mixture into a sieve lined with cheesecloth and place it over a bowl to drain. Pull the corners of the cloth together, squeeze out excess whey, add any optional ingredients you prefer, and then either use the ricotta immediately or spoon into an airtight container and refrigerate for up to four days.