Blend milk, cream, and salt in lg heavy pot.  Bring to boil over med. heat, stirring occasionally to prevent scalding, approx. 10 min.

As soon as mixture boils, reduce heat to low.  Stir in lemon juice.  (The citric acid is what causes the cheese to curdle, so don't skimp here.)

Stir occasionally until mixture curdles, approx. 5-6 min.  

Pour mixture into colander lined with cheesecloth over lg bowl in sink.  Let drain until ricotta thickens to your desired consistency, approx. 1-2 hrs.  (If drier ricotta is needed, you can continue to drain it in the refrigerator.) 

Transfer ricotta to airtight container(s) and refrigerate until ready to use; it should keep 2-3 days.  Discard whey or reserve for another use.