This recipe uses Amer Picon which is a bittersweet French orange-flavored aperitif. It is a common bottle throughout Europe, less so in the USA.
Take a sip on this one . . . close your yeux . . . écouter . . . et voilà vous êtes en France. Santé!
Combining tequila, Chartreuse and Amer Picon might seem bold, but the cocktail it results in is so nice!