The European tradition of making bittersweet liqueurs-called amari in Italian-has been around for centuries. But it is only recently that these herbaceous digestifs have moved from the dusty back bar to center stage in the United States, and become a key ingredient on cocktail lists in the country's best bars and restaurants. Lucky for us, today there is a dizzying range of amaro available-from familiar favorites like Averna and Fernet-Branca, to the growing category of regional, American-made