This was a team effort. I made the beef stock. My wife, with her usual expert attention to detail, finished the soup. As her reference, she used The New Best Recipe, from the editors at Cook's Illustrated magazine. A small controversy arose, as the good editors at Cook's Illustrated felt compelled to give a recipe substituting a mix of store-bought chicken stock, beef stock and red wine for an authentic beef stock.
My wife happens to believe that if this gets harried cooks to attempt a French onion soup, all the better. My personal opinion is, I don't really have an opinion. It just seems to me that the time it takes to gather up the ingredients for a faux-stock could just as easily be spent gathering up the ingredients for a real stock. Really, there is not that much extra effort involved and a homemade beef stock will send you into orbit, it is that good.
Once you've settled the matter of a stock, the soup is fairly simple. Slice five red onions thinly and saute them with two tablespoons butter and 1/2 teaspoon salt in a heavy pot at least 30 minutes, stirring frequently, or until the onions are extremely soft, reduced and syrupy. Add 6 cups stock and 1/4-cup red wine, plus 2 sprigs parsley, 1 sprig thyme, 1 bay leaf.
Scrape the onions from the bottom of the pot. Bring the soup to a boil, then reduce heat and simmer for about 20 minutes. Stir in 1 tablespoon balsamic vinegar and season with salt and freshly ground black pepper as needed.
To finish the soup in the traditional French style, ladle it into six deep ceramic bowls and place two slices of baguette, cut on an angle, on top of each. Over the bread, distribute Greyere and Asiago cheese, approximately 4 1/2 ounces Gruyere and 3 ounces Asiago total.
My wife was able to use our cheese slicer--the kind with a taught wire on the handle--to make very thin slices out of the Gruyere. She grated the Asiago. But however you manage it will be fine, since the cheese melts in the oven. My wife simply dislikes those presentations where the cheese is melted in big globs on the edge of the soup bowl, and cheese is running down the sides (remember, you do have to clean the bowls afterwards).
Now place the soup bowls on a baking sheet and put them under the broiler until the cheese is melted, browned and even charred a little in picturesque fashion. Carefully place the hot bowls on an underliner to bring to the table and serve with your favorite red wine.
The soup is a meal in itself. When you think about it, between the bread, the cheese, the onions and the beef, virtually all the major food groups are represented. But we went ahead and served a salad afterwards with a variety of winter greens, dried cranberries, a leftover lump of Feta cheese and a honey-mustard vinaigrette. We had a bunch of bananas going bad, so my wife made our favorite banana bread with chocolate nibs for dessert, served with a dollop of vanilla ice cream.
This was a simple meal, but a perfect Sunday supper. I urge you: should any beef scraps fall into your hand--or bones--make beef stock. You will not regret it.