Step 1

To salt-rim the glasses, rub a cut lime around the rim of each of 4 stemmed goblets. Fill a saucer with salt. Dip goblet, upside down, into salt. Refrigerate goblets until ready to use.

Step 2

Fill blender three-quarters full of ice cubes. Pour lime juice, tequila, and Cointreau over ice. Add sugar; blend, starting slowly, and then increasing to high speed, until ice is very finely chopped and mixture is frothy. Taste for sweetness; add more sugar if desired. Blend a few seconds more; pour into salt-rimmed glasses. Serve immediately.