Carefully crush a candy cane into small pieces. Spread powder onto a small plate. Rub a lime wedge around the rim of your glass, then dip in the powder to coat. Set aside.
Add ice to a cocktail shaker. Pour vodka, cranberry juice, lime juice, & optional Cointreau inside. Add lid and shake until your hands are cold, about 20 seconds.
Strain cocktail into prepared glass. Zest reserved lime over top. Garnish with cranberries if using and serve immediately.