Have four 8 oz cocktail glasses chilled and ready.
Strain the chilled simple syrup through a fine mesh sieve into an airtight container or glass jar. Discard lemon zest.
In a shaker filled with ice, add ¼ cup (63 ml) of the gin, 2 tablespoons (30 ml) of the cranberry juice, and 1 tablespoon of the lemon simple syrup. Shake vigorously, and strain into a chilled glass. Repeat process another 3 times for the remaining cocktails. Top each glass with about ⅓ cup (83 ml) of the chilled sparkling wine.
Garnish with fresh cranberries and/or lemon zest, if desired.