Line a large sieve with layer of heavy-duty (fine-mesh) cheesecloth and place over a large bowl.

Slowly bring milk, cream, and salt to a rolling boil in a 6-quart heavy pot over moderate heat, stirring occasionally to prevent scorching.

Add lemon juice and reduce heat to low. Simmer, stirring constantly, until liquid curdles, about 2 minutes.

Pour the mixture into the lined sieve and let it drain 1 hour. Discard liquid, place ricotta in a covered container and chill in refrigerator. Will keep for 2 days.