Line a fine-mesh sieve with 2-3 layers of cheesecloth, making sure there's enough overhang to gather later. Place the sieve over a large bowl to collect the whey.

In a large, heavy-bottomed pot, combine the whole milk, heavy cream (if using), and salt. Stir gently to combine.

Heat the milk mixture over medium-high heat, stirring occasionally to prevent scorching on the bottom. Continue heating until it reaches a temperature of 195-200°F (90-93°C). It should be steaming heavily and just beginning to show small bubbles around the edges, but do not let it come to a rolling boil.

Remove the pot from the heat. Gently pour in the lemon juice or white vinegar, stirring just once or twice to incorporate. Let the mixture sit undisturbed for 10-15 minutes. During this time, the milk solids (curds) will visibly separate from the greenish-yellow liquid (whey).

Using a slotted spoon, carefully scoop the curds from the pot and transfer them to the prepared cheesecloth-lined sieve. Try to get as much of the solid curds as possible, leaving the whey behind.

Let the ricotta drain in the sieve for 15-30 minutes, or longer if you prefer a drier, firmer ricotta. The longer it drains, the thicker it will become. For a creamier, softer texture, drain for less time.

Transfer the fresh ricotta to an airtight container. Use immediately or refrigerate. Enjoy your homemade ricotta!