The secret to this classic is long, slow cooking of the onions to allow their natural sugars to caramelize; this gives the soup its characteristic depth of flavor and mahogany color.
How to make it:
Heat in a soup pot over medium heat until the butter is melted: 2 tablespoons of butter / 2 tablespoons of olive oil.
Add and stir to coat: 5 medium onions, thinly sliced /Pinch of dried thyme. Cook stirring occasionally, and keeping a vigilant eye on the onions so they do not scorch, over medium heat.
As soon as they start to brown, after about 15 minutes, reduce the heat to medium-low and continue to cook, covered, stirring more often, until the onions are a rich brown color, about 40 minutes.
Stir in: 2 tablespoons of dry sherry or cognac. The heat will evaporate the liquor leaving the flavor.
Increase the heat to high and cook, stirring constantly until all the sherry has cooked off.
Stir in: 3 and a half cups of brown beef stock. Bring to a boil, reduce the heat and simmer, partially covered, for 20 minutes.
Season with: 1 to 1 and a half salt / 1/4 to 1/2 teaspoon black pepper.
Place 8 ovenproof soup bowls or crocks on a baking sheet. Ladle the hot soup into the bowls and top each bowl with: 1 to 3 slices of french bread, toasted if fresh.
Sprinkle each bowl with: 3 tablespoons Gruyere cheese.
Broil or bake in a 450 degree oven until the cheese is melted and starting to brown. Serve immediately.
Note: This recipe is from ” Joy of Cooking”. This old warhorse cookbook taught me to cook. Enjoy in good health.