I'd suggest using 2 hands if possible, but it's often not an option when you might need to draw it. When using a cover garment in competition, I use on hand to throw my jacket or shirt out of the way. I make sure to get a deliberate movement of the coat and index my grip as fast as possible. I'm by no means the fastest draw around, but it works for me and it's fairly deliberate. Clear the cover shirt etc... index a solid grip and draw the pistol.
I find using 2 hands to draw is more cumbersome with a coat, but it seems to work well if my shirt is buttoned up as it can't really be thrown out of the way like a coat.