Add ice to a martini glass and fill with water. This will chill the glass while you make the cocktail.
In a cocktail shaker add ice, vodka, apple juice, elderflower liqueur, and juice from 1/4 of a lime. Shake until well blended.
Discard ice and water from martini glass and strain the drink into the glass.
Garnish with an apple slice (optional) and enjoy!