Add the broth, lemon juice, and salt to a pot and bring to a boil over medium-high heat.
While the broth is heating, in a blender or food processor, puree the avocados with the cream until smooth.
Once the broth is boiling, remove from the heat and stir in the avocado mixture.
Refrigerate until chilled. Serve well chilled.
Notes
Make sure to blend to avocados until completely smooth or use an immersion blender once mixed into the broth.
Do not serve the soup heated. If you prefer it slightly warmer, you can let it sit at room temperature for a few minutes, but avoid heating it on the stove or in the microwave, as this can cause the avocados to brown and the texture to change.
Before storing leftovers, pess plastic wrap directly onto the surface of the soup before refrigerating to help prevent browning.
Use ripe avocados for the best creamy texture and rich flavor.