This also works quite nicely as a broth to cook mussels in.
Croutons
1 Loaf of French Bread
Black Truffle Oil
Pepper
6 Slices of Swiss Cheese (or Gruyere)
If you don't have beef stock handy, about now's a good time to get 5 cups of water simmering with 3 cubes of beef bouillion. If you do have beef stock, carry on.
Throw in your butter (I usually cut it into a few smaller pats so as to help it melt more quickly), olive oil, and bacon grease (or add a little more olive oil if you don't have any bacon grease), and set your flame to high. This will cook for around 15 to 20 minutes, and you'll want to stir it somewhat frequently to prevent the onions from burning to the bottom of the pot.
While this is going on, thinly slice your garlic (or dice it up, whichever you prefer). Once your 15 - 20 minutes are up on the onions, add the garlic and your sugar to the stock pot and reduce the heat to medium. Continue stirring, and let cook for another half hour to 45 minutes.
While all this is going on, you'll want to find a throw-away wooden skewer, a very long match (like the kind to light fireplaces), or one of those long lighters for lighting a barbeque. Read on.
After the half hour or so is up, you want to pour in the cognac. Once you do that, you want to flame it off - thus needing something longer than your standard match (so that you don't take all the hair off your arm by reaching into the pot). Let the flames subsist, add in your salt, pepper, thyme, mustard, and flour, and stir so as to get the onions and garlic coated.
Next, pour in your champagne (or white wine), and your 5 cups of beef stock. Once this comes to a simmer, drop the heat to medium-low, and continue to simmer for 20 minutes or so.
As the soup is simmering, take the loaf of French Bread and cut it into slices on a digaonal. Lay these slices onto a cookie sheet, and drizzle a little bit of truffle oil over each, rubbing it in with your fingers. Crack some black pepper over each, and put pieces of your cheese on each.
Around now is as good a time as any to drop things into a holding pattern if you're waiting on guests or just want a brief respite from the kitchen and need a drink.
Alternately, you can pre-heat the oven to 375° so you can cook your croutons.
OK - if it's showtime, pop your cookie sheet with the croutons on it into the oven, and let cook for around 15 minutes or so, until the cheese is good and melty and bread toasted.
To serve, stir a ladel around in your pot to insure you get a decent portion of onion, and pour into a bowl (and maybe an extra ladel of the broth). Place a crouton on top, and serve!