Prepare elongated wine glasses, and put between 1/3 to 1/2 the size of the glass of ice in each one. Clap the mint leaves between your hands and place 2 or 3 large ones in each glass, so that the leaves release all their scent and flavor.
Place 1 to 2 slices of lime in each glass, inside, or to decorate the rim. Pour 1 tablespoon of elderflower syrup in each glass.
Fill about half the glass with cava and the rest with soda. Stir very well so that the syrup dissolves throughout the glass and enjoy.