2 oz. bourbon
½ oz. pimento (allspice) dram
¾ oz. fresh lime juice (~1 lime)
¼ oz simple syrup
1 dash Angostura or orange bitters

(Tweak pimento dram and lime juice to taste)

(Can drop the simple syrup and replace bourbon with rum)

(a dash of Benedictine DOM also rounds it out well)

Some history: http://badassdigest.com/2012/09/14/your-guide-to-drinking-this-w...