Cut avocados in half and remove pits. Using a spoon, scoop out the flesh and drizzle with lemon juice.
In a food processor or blender, combine avocado and condensed milk. Blend until smooth and no avocado chunks. Transfer the mixture to a large bowl.
In another bowl, add heavy cream. Using a hand mixer at low speed, beat mixture until it begins to thicken. Increase speed to medium and continue to beat for about 8 to 10 minutes or until stiff peaks form.
Add ⅓ of the whipped cream to the avocado bowl and gently fold in until there are no visible white streaks, making sure not to deflate the whipped cream. Repeat with another ⅓ of whipped cream and then the remaining ⅓ of the whipped cream.
Transfer the mixture into a loaf tin. Cover with plastic wrap, pressing down film onto the surface of the mixture.
Freeze for at least 6 hours or overnight until firm. Serve frozen.
Drizzle the avocados with lemon juice to keep from browning.