Black Powder pass does not really have a trail over it on the French Gulch side. It is a big carry and not recommended.
You can take several ways over the ridge that separates the Swan and French drainages (the Golden Horseshoe) but the method described above going up American/Georgia gulch road is the most strait forward. (go down the Little French flume rather than the Humbug Jeep road) Climb Sally Barber and from the top of that, keep climbing nightmare on Baldy. From there you can take the Firecracker course in reverse to Bakers Tank trail which will dump you out on Boreas Pass rd about 3.5 miles from the summit. The Gold Dust trail is much preferred for getting down to Como over the rd.