I think with modern aircraft assists do allow you to fly one handed although just like when I used to race cars whilst I could in theory steer with one hand I always had both for precision control. Back in the day I believe they would fly one handed whilst relaxed and then as has been stated under load or stressful situations two hands were used except where throttle adjustments where needed. Maybe need Chowbirds take as he's our resident commercial flyer- do you fly one arm on the yoke and the other on the side of the window???
That all said these guys seem to be one handed flyers: