In a large pitcher, combine elderflower syrup, cranberry juice, and freshly squeezed lemon juice. Stir well until all the ingredients are well incorporated.
Fill serving glasses with ice cubes.
Pour the elderflower and cranberry mixture into each glass, filling them about two-thirds full.
Top each glass off with sparkling water, giving it a gentle stir to combine.
Garnish each glass with fresh mint leaves and a slice of lemon on the rim.
Serve immediately and enjoy the refreshing taste of winter.