Run a lemon wedge along the rim of your martini glass to moisten it.
Pour sugar onto a small plate, then dip and gently twist the rim of the glass in the sugar until evenly coated. Set aside.
In a cocktail shaker, add vodka, triple sec, lemon juice, and simple syrup.
Fill the shaker with ice and shake vigorously for 10–20 seconds until well chilled.
Strain the mixture into your prepared sugar-rimmed martini glass.
Top with a small scoop of lemon sorbet for a refreshing twist, and serve immediately.