Chill 4 martini glasses. In a small shallow dish combine the sugar and the lime zest. Run the lime wedge around the rim of each glass. Dip in the sugar and zest mixture.
In a cocktail shaker mix the cognac, Triple Sec, sweet and sour mix, Limoncello, and lime juice over ice. Shake to chill.
Pour the Side Car Martinis into the glasses and serve immediately.