Cut each avocado in half, remove the pit, and scoop the flesh into your blender. Discard any brown or stringy spots.
Add the sweetened condensed milk, whole milk, lime juice, and pinch of salt.
Blend on low, then increase to high for 45-60 seconds until completely smooth and creamy, scraping down the sides once if needed.
Add the ice cubes and blend on high 30-45 seconds until the ice is fully crushed and the smoothie is thick and frosty. Taste and blend in more condensed milk a tablespoon at a time if you want it sweeter.
Pour into tall glasses. Drizzle with condensed milk and serve immediately with wide straws.