Step 6: Broil
WATCH CLOSELY. The only time I've ever burned anything is when I use the broiler! Things can be bubbling along happily, then you walk away for 30 seconds and BAM your oven is on fire.
After a few minutes, the cheese will be all bubbly and melted and slightly browned. The bread will be toasty. (Might take a little longer if you don't have a broiler, but I wouldn't know.)
At this point, take the soups out of the oven. And you're done! Be careful serving, as they are very hot. But I hope you could figure that out on your own.
Enjoy your delicious French Onion Soup!