Pour 1/4 of the lemon juice into a small bowl and the salt onto a small plate. Dip a glass into the lemon juice, opening downwards, so that the rim is moistened.
Strain it into the salt, do the same with the second glass and put them in the freezer while you prepare the rest.
Blend the blueberries in a blender and strain through a fine sieve.
Pour the blueberry juice into a shaker, add the rest of the ingredients, 1 tablespoon of each balsamic, and the ice cubes then shake.
Pour the mixture into the two glasses, add some balsamic pearls and serve.