For each drink, combine 4 ounces of mixer with 2 ounces of vodka in a cocktail shaker with ice; strain into a chilled martini glass.
* Finely grated zest of 1 orange
* Finely grated zest of 1 lime
* 1/2 cup sugar
* 2 1/2 cups cranberry juice
Bring zests, sugar, and 1/2 cup water to a boil, stirring.
Reduce heat; stir until sugar has dissolved.
Put juice into a large container; stir in zest mixture.
Refrigerate, covered, 1 hour or overnight.
Strain; pour into an airtight bottle.
Mixer can be refrigerated up to 1 week.