Line colander with four layers of cheesecloth or 2 layers of food-safe paper towels and set over large bowl.
Combine milk, salt, and vinegar or lemon juice in microwave-safe glass 1-quart liquid measure.
Microwave on high heat until lightly bubbling around edges, 2 to 4 minutes (milk should register about 165°F on an instant-read thermometer).
Remove from microwave, and stir gently for 5 seconds. Milk should separate into solid white curds and translucent liquid whey. If not, microwave for 30 seconds longer. Repeat until fully separated.
Using slotted spoon or wire skimmer, transfer curds to prepared colander, cover exposed top with plastic wrap, and allow to drain until desired texture is reached.
Under 5 minutes extremely moist and creamy: Best for immediate consumption, while still warm. For savory applications, drizzle with olive oil, sprinkle with sea salt and black pepper, and serve. For dessert, drizzle warm ricotta with honey, and serve with fruit.
15 to 20 minutes small, tender curds with a cottage cheese-like consistency. Moist and spreadable, but not runny. Best for moist savory applications like lasagna or ravioli fillings and dips, or certain uncooked pastry applications, like cannoli filling.
2 hrs to overnight (in fridge) firm, dry, crumbly curds that can easily be molded into firm shapes. Best for pastry, such as ricotta pancakes, ricotta gnocchi, or ricotta tortas.
Store in covered container in refrigerator for up to 5 days.