French Onion Soup

Serves six.

4 tablespoons unsalted butter
3 large white onions (about 2 1/2 pounds), thinly sliced
1/2 cup plus 2 tablespoons Madeira
4 cups chicken stock
4 cups beef stock
salt and pepper
2 tablespoons balsamic vinegar
six thick slices stale sourdough bread
2 cups grated Gruyere cheese (about 6 1/2 ounces)
2 scallions, chopped

Melt the butter in a large saucepan. Add the onions and cook over
moderately high heat, stirring frequently, until softened and starting to
brown, about 15 minutes. Add 2 tablespoons of the Madeira, reduce the heat
to moderate and cook until evaporated. Continue adding a total of 1/2 cup
of the Madeira, 2 tablespoons at a time, stirring often and cooking until
evaporated before adding more, about 15 minutes. Continue cooking the
onions, stirring, until deep brown, about 10 minutes more.
Add the chicken and beef stocks to the saucepan and bring to a rolling boil.
Reduce the heat to low and simmer until the soup is flavorful and the
onions are tender, about 1 hour. Season with salt and pepper and stir in
the balsamic vinegar and remaining 2 tablespoons of Madeira.
Preheat the broiler. Arrange 6 oven-proof bowls on a baking sheet. Divide
the soup among the bowls, top each with a bread slice and cover the bread
with the cheese. Broil for 1 to 2 minutes, until the cheese is golden and
bubbling. Garnish the soup with the scallions and serve.

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