The guadalajara is a rare sparkling tequila cocktail, found on the inimitable cocktail virgin blog and attributed to bar manager ashish mitra at bostons russell house tavern. Its a tremendously refreshing drink, with the crispness of the mint and the lemon and bubbly bringing out the bright vegetal notes of the tequila. You could get away with an aged tequila, but blanco is best here if you have it.