To prepare the lemon shells for serving, cut off a thin slice from the tip of each lemon, about one-fourth of its length. Keep the tips aside. You will need them later.
Carefully juice the lemons, making sure the shells stay intact. Keep the juice aside to use later.
Use a small spoon to scoop out any leftover pulp. Rinse the shells under water and pat them dry.
In a blender, combine the lemon juice, water, and agave syrup (or sugar). Blend until well combined and smooth. Transfer the mixture to another container and chill for 4 hours, or until it is icy.
Pour the mixture into an ice cream maker and churn until it reaches a sorbet-like consistency.
Add a scoop of sorbet to each lemon shell. Add another scoop on top if you want the lemon shells to look fuller. Repeat with all the lemon shells.
Top each lemon shell with the lemon tip you cut in Step 1 and a few mint leaves.
