Serves 6.

INGREDIENTS
3/4 cup balsamic vinegar

1 1/2 cups water

2 large onions, sliced thin (about 4 cups)

1/3 cup sugar

4 teaspoons chopped fresh rosemary leaves plus 12 sprigs

2 cups low-salt chicken broth

1 cup heavy cream

six 10-ounce trout, cleaned, leaving heads and [...]