Ricotta is a soft, fresh Italian dairy product made not from milk but from whey — the watery liquid left over after other cheeses are made. Milky-sweet, mild and barely salted, it is a loose mass of fine, moist, slightly grainy white curds, the everyday filling of lasagne and ravioli, the heart of cannoli and cheesecake, and a fixture spread on toast under a drizzle of honey.