1. For the simple syrup: In a small saucepan, whisk together the sugar and 1 cup water over medium heat. Cook, stirring occasionally, until the sugar is completely dissolved, 2 to 3 minutes. The syrup should be clear, not cloudy. Remove from the heat and let cool completely, about 1 hour on the counter or 30 minutes in the refrigerator. Store in an airtight container in the refrigerator until ready to use. 2. For the mistletoe martini: To make the garnish, thread a toothpick with 1 cranberry, 3 mint leaves, and a second cranberry, fanning the mint leaves out. Repeat with a second toothpick and the remaining cranberries and mint.  3. Fill a cocktail shaker halfway with ice. Add the cranberry juice cocktail, vodka, elderflower liqueur, lemon juice, and 1 ounce simple syrup (reserve the remaining syrup for another use). Cover and shake vigorously until cold, 10 to 20 seconds. Strain into 2 martini or coupe glasses and garnish with the cranberry and mint picks.