I've been making this for years. It's been a restaurant favorite of mine since I was a kid. Very easy to make.
First the onion soup:
Just thin-slice up some half onion rings (two onions will do for two servings).
Place them in a medium hot, buttered, pot.
Saute till thoroughly cooked.
Add beef broth (I use one can of condensed Campbell's) and bring to boil.
Add a quarter cup of Madeira wine to the bottom of two oven-safe bowls appropriate for French Onion Soup. They make specialized bowls for this, but all sorts of bowls will do, so long as they are deep and relatively narrow-mouthed.
Add enough soup to each bowl to come up two-thirds to the top. Taste and adjust salt to liking.
Add a hard roll (cut to fit the bowl, if necessary) or a section (or two, or three, depending on dimensions) of a French baguette. Push it down into the soup so it's close to level with the top of the bowl.
Top with either Swiss or Gruyère cheese. I use a good bit.
Place bowls on an aluminum foil covered cookie sheet or baking pan and place into a 400 degree, preheated, oven for 10 to 15 minutes (check after 10 minutes).
Serve.