Ingredients

　　1 tablespoon butter

　　3 large yellow onions, very thinly sliced

　　1 teaspoon balsamic vinegar

　　3 2/3 cups beef broth (two 14 1/2-ounce cans)

　　1/2 cup whole-wheat croutons

　　1/4 cup grated Parmesan cheese

　　Preheat a nonstick Dutch oven over medium-high heat. Add the butter and onions. When the butter has melted, stir, cover, and cook until the onions are limp and beginning to brown, 4 to 5 minutes. Stir in the vinegar. Add the broth, and bring to a boil. Reduce the heat to low, re-cover, and cook for 20 minutes more. Divide the croutons among 4 warmed soup bowls, ladle the soup on top, and sprinkle 1 tablespoon Parmesan cheese over each.

　　Cooks' Note

　　Use either homemade beef broth (see page 28) or canned for this soup. Be sure to cook the onions until they are golden brown and slightly caramelized to bring out their natural sweetness; the addition of balsamic vinegar boosts the sweetness even more. If your market doesn’t carry whole-wheat croutons, make your own by toasting 2 slices of stone-ground whole-wheat bread, trimming off the crusts, and cutting into the desired size croutons.

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