Suzanne Smith, the casting director for Outlander, recently said that the process was really pretty simple.
The creator, who has been a part of the show since the beginning and who also cast Sam Heughan as Highlander hero Jamie Fraser, discussed bringing Menzies on in an exclusive interview with Daily Express.
Since Claire first gets confused when she travels through the stones and confuses Black Jack for her husband Frank dressed in historical attire, the Starz series was always on the lookout for one actor to play both roles.
The search for the ideal actor was handled in two scenes, Smith stated. One with Black Jack and one with Frank, and from what I can recall, the Black Jack part was a lengthy session in which [Menzies] seemed to be a one-take wonder.