Set a large heavy-bottomed pot with 4 cups whole milk, 1 cup heavy cream, and ½ teaspoon kosher salt over medium-high heat. Insert a cooking thermometer inside the pot to monitor the temperature.
Heat, stirring occasionally to prevent scorching, until the mixture reaches 185 - 190°F. It should be steaming, with small bubbles and foam across the surface, but should not reach a full boil. This may take 10 - 20 minutes.
Maintain the temperature between 185 °F - 190 °F for 3 - 5 minutes, and continue stirring. If needed, lower the heat to maintain that temperature.Note: If desired, you can add more salt here to taste. Spoon a bit of the milk into a bowl, let it cool slightly, then taste to see if you want more salt.
While stirring, slowly pour in 2 tablespoons vinegar or3 tablespoons lemon juice until the mixture begins to curdle. You should see white curds separating from the translucent yellowish whey. Immediately stop stirring and remove from the heat.Note: If the mixture doesn’t curdle at all, keep stirring over the heat, then add 1 tablespoon vinegar (or 1 tablespoon lemon juice) until it begins to separate. If needed, continue adding only 1 teaspoon of acid at a time until the mixture separates. Then immediately stop stirring and remove from the heat.
Allow the mixture to sit for 10 minutes; it will continue to separate over time.Note: If the mixture still looks very milky, you can add another teaspoon of vinegar or lemon juice to the pot and return the pot to medium heat. As the mixture heats, it should begin to curdle more. Remove from the heat once it curdles, then wait for another 10 minutes before proceeding to the next step.
Meanwhile, set a fine mesh sieve over a large pot. Line the strainer with two layers of cheesecloth.
Use a slotted spoon to scoop the solid curds from the pot into the cheesecloth. Note: Using a slotted spoon instead of pouring everything into the cheesecloth helps preserve the texture and speeds up the draining process.
Let the ricotta drain in the cheesecloth to your desired consistency (5 - 10 minutes for soft ricotta or 20 - 30 minutes for firmer ricotta), then transfer to an airtight container in the fridge until ready to use. The leftover liquid, or the whey, can be discarded or saved for another use.
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Notes
Tips:
Do not use ultra-pasteurized milk. Ultra-pasteurized milk has been heated to a high enough temperature to denature some of the milk proteins, meaning the milk may not coagulate properly. Regular pasteurized milk is totally fine, as is homogenized or non-homogenized milk.
Whole milk is recommended. You can make ricotta with 2% milk (for a slightly less creamy texture), but anything lower will result in a poor yield.
Lemon juice vs. vinegar: White distilled vinegar is slightly more acidic than lemon juice. Lemon juice has a stronger flavor. Depending on the use case, it might be nice to have additional notes of citrus (though you will need more lemon juice to curdle the milk). To keep things simple, just use vinegar.
A cooking thermometer is highly recommended to maintain an optimal temperature. I've found that 185°F (85°C) to 190°F (88°C) is a good sweet spot, where you'll have a good yield of creamy, fluffy ricotta. If you end up a little above or below (195F or 180F), that's okay too. Where you start to affect things is when you're significantly above or below the 185°F (85°C) mark.
Storage: Store ricotta cheese in an airtight container for 4 to 5 days in the fridge.
Leftover whey can be used in smoothies. You can also use it in place of water in many cases, such as cooking rice or other grains and potatoes.