1.5 oz lime juice (a little less than the juice of two limes)
1 oz Cointreau
2 oz white tequila (e.g. Corazon blanco)
1 cup ice
Dampen the edges of the glasses with the remains of one of the juiced limes. Place some salt or sugar on a plate, and dip the rims of the glasses in it. If you want you can add lime zest into the salt or sugar.
Add all liquid ingredients into a cocktail shaker or blender. 1 cup of ice in the blender will create a very liquidy drink. Add an additional half cup of ice if you prefer a more frozen drink. Pour mixture into the glasses.
Note: limes are easier to juice if you microwave them for 15 seconds and/or roll them on the counter top before you cut them in half and squeeze them.