Line a colander with a triple layer of cheesecloth and set in sink. In a liquid measuring cup, combine lemon juice and vinegar.
In a Dutch oven or large saucepan over medium-high heat, heat milk and salt to 185 degrees. Stir frequently with a rubber spatula to prevent scorching.
Remove pot from heat and gently stir in lemon juice and vinegar until the mixture curdles, about 15 seconds.
Let rest, without stirring, until the mixture fully separates into solid curds and translucent whey, 5 to 10 minutes.
If curds do not fully separate the whey looks milky, stir in 1 tablespoon of vinegar and let sit 2 to 3 minutes longer. Repeat this process until curds separate.
Gently pour prepared mixture into prepared colander. Let rest, without moving, until whey has drained from edges of cheese but center is still very moist, about 8 minutes.
Gently transfer cheese to large bowl, keeping as much whey in center of cheese as possible. Stir well to break up large curds and incorporate whey.
Refrigerate until cold, about 2 hours, or up to 5 days. Stir ricotta before using.
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Notes
Milk: Use pasteurized (not ultra-pasteurized / UHT) whole milk.
Lemon juice: Use regular lemons (not Meyer lemons; they don't have enough acid to curdle the milk).
Yield: This recipe makes 2 pounds (4 cups) of ricotta cheese, or 32 (1-ounce) servings (2 tablespoons each).
Storage: Store ricotta covered in the refrigerator for up to 5 days.
Leftover whey: Add it to smoothies for a protein boost or use it in place of water when making bread and pizza dough (it feeds the yeast).