I chose amaro Averna Siciliano in this cocktail because of the undertones of orange and caramel that this liqueur presents. Any deviation from this amaro is therefore not ideal but the closest acceptable alternatives would be amaro Nonino or amaro Montenegro. Definitely do not use Campari, Aperol or Fernet Branca. Each of these Italian bitters has a wildly different flavour profile to Averna and would alter the cocktail significantly.