Combine the Absolut Citron, Triple sec and juice of 1/3 lemon (~3/4 oz juice) in a cocktail shaker half-filled with ice cubes. Shake. Use the lemon to wet the edge of a chilled martini or cocktail glass, and dip the glass in sugar to coat the rim. Strain the mixture into the cocktail glass, garnish with a lemon twist, and serve.