Stir ingredients with ice, strain into Nick & Nora or other cocktail glass. Express orange peel over drink.
This is a very dark riff on the Negroni. Aquavit is playing the part of gin, Black Balsam provides the bitter backbone, and the Mirto is a somewhat herbal berry liqueur replacement for a full bodied vermouth such as Carpano Antica.
I have become a fan of Mirto in various concoctions of my own. Riga Black Balsam has been trickier to find mates for, but I recently realized that Mirto could stand up to the earthy/clay bitterness of the Black Balsam and play off of one of its components. Mirto is a myrtle berry liqueur, while one of Black Balsam's key ingredients is "golden withy", better known as bog myrtle--I assume the golden refers to the buds/flowers.
I considered gin or aquavit for a Negroni style equal parts cocktail, and chose Ahus Akvavit as it has a milder, lighter herbal profile than something like Linie. (I also tried Ransom Old Tom Gin but there was too much going on in the way of aromatics.) Since Riga and Stockholm (Ahus) are both along the Baltic Sea and the color of the cocktails is a very dark, nearly fully opaque brown, I decided to dub the libation a Baltic Black Negroni. (The Sardinian mirto is the tie back to Italy.)
The orange twist and orange bitters round out the flavor by accentuating the Seville orange essence in the Ahus.