In a blender cup, combine tequila, simple syrup, cointreau, lime juice, egg white, and 1 cup of ice.
Blend baby blend for at least 30 seconds. The margarita should be slightly slushy, but not resembling a frozen margarita (this is just so that we are drinking the COLDEST possible drink without watering down)
Pour into two cocktail glasses, top with an ounce of sparking water, and CHEERS!
Keep the blender out, because you'll want another 😉