Fill shaker halfway with ice. Add vodka, elderflower liqueur, cranberry juice, lime juice, and simple syrup.
Shake hard for 15–20 seconds until chilled.
Strain into a chilled martini glass.
Garnish with cranberries or lime wheel.
Notes
Swap elderflower liqueur for gin for a more herbal, dry martini. If using sweetened cranberry juice, reduce simple syrup. Serve immediately, well-chilled.