Shake with ice, strain into coup.
UPDATED/CURATED: Replaced KC contributor's proportions with those published in an article later in 2013. The main difference is a reduction in Averna from 1 oz to 1/4 ounce.
Also, the original recipe used 2 dashes of a cardamom tincture (recipe below), although 2 dashes of Scrappy's Cardamom Bitters also works well.
Cardamom tincture: Add 1/2 cup cardamom pods to 1 cup of a high proof neutral spirit. After five hours pods should be open and tincture should be a greenish hue. Strain/filter the tincture, leaving it in contact with the pods too long will make it too bitter.
The original posting on KC was an attempt to reproduce a cocktail that KC member candlepowerdiety had at the Beretta in San Francisco several months earlier. It was very close, other than using 1 oz of Averna, vs. 1/4 oz in the authentic recipe, and using only one dash of cardamom bitters vs. 2 dashes of tincture.