The Brooklyn is a classic cousin of the Manhattan that isn’t as well-known as it ought to be. This is probably due to the relative obscurity of Amer Picon, an amaro with dominant notes of orange peel, gentian, and quinquina. It’s not well-known or particularly easy to find outside of France, but it’s worth the search!
If you can’t find Amer Picon, other orange-forward amari like Amaro CioCiaro or Ramazotti or even Amaro Nonino (our personal favorite, though it is sweeter) will do. Some recipes call for a substitute of Punt e Mes vermouth or just a couple dashes of bitters, but in our opinion you’re better off just making a different drink if you don’t have a good orange amaro on hand.