Admittedly, there's nothing really Mexican about this cocktail besides the tequila.
But that's okay - it tastes really-really-really good. That's enough for it to be a fiesta at my house.
You want this to taste like plum, so use a decent-sized one, not one of those tiny (but delicious) little plums.
1 ounce tequila
1/2 ounce simple syrup
1/4 ounce grenadine
Wedge of lime for garnish
Remove the pit from the plum, cut it into chunks, and drop it into you blender. Add the tequila and blitz it up until it's mostly smooth. You'll have flecks of skin, but that's fine.
Pass the mixture through a fine strainer and into a cocktail shaker. See? No more flecks of skin.
Add the simple syrup, grenadine, and half a tray of ice. Or a good hand full of ice if you live in a world of modern conveniences like ice makers.
Put the cover on the shaker, shake-shake-shake, and strain it into a pretty glass. Garnish with the lime.