While the "sour" part of this cocktail usually comes from lemon, a splash of grapefruit juice might make it even better (and more mouth-puckering). While it's not a drastic deviation, this zingy ...

And when I do, more often than not, I include this vegan, gelatin-free, sour grapefruit candy. It's an old standby that delivers a bracing hit of citrus, acid, and just the slightest undertone of ...