Mix all ingredients, except for the soda, in a cocktail shaker with some ice. Pour into a glass filled with ice and top up with soda.
Tip: There are also variants of the cocktail in which elderflower liqueur is used instead of elderberry syrup. For me personally he becomes too alcoholic. I`ve also seen recipes that leave out the sugar syrup. My absolute favorite cocktail, not too sweet, nice and refreshing and, above all, fruity.